Subsurface Location Research Articles

Locating near-surface scatterers using non-physical scattered waves resulting from seismic interferometry

Abstract We use controlled-source seismic interferometry (SI) and inversion in a unique way to estimate the location of near-surface scatterers and a corner diffractor by using non-physical (ghost) scattered surface and body waves. The ghosts are arrivals obtained by SI due to insufficient destructive interference in the summation process of correlated responses from a boundary of enclosing sources. Only one source at the surface is sufficient to obtain the ghost scattered wavefield. We obtain ghost scattered waves for several virtual-source locations. To determine the location of the scatterer, we invert the obtained ghost traveltimes by solving the inverse problem. We demonstrate the method using scattered surface waves. We perform finite-difference numerical simulations of a near-surface scatterer starting with a very simple model and increase the complexity by including lateral inhomogeneity. Especially for the model with lateral variations, we show the effectiveness of the method and demonstrate the estimation of the subsurface location of a corner diffractor using S-waves. In all models we obtain very good estimations of the location of the scatterer.

LipL32 Is a Subsurface Lipoprotein of Leptospira interrogans: Presentation of New Data and Reevaluation of Previous Studies

The agents of leptospirosis, a zoonosis with worldwide distribution, are pathogenic spirochetes belonging to the genus Leptospira. The leptospiral life cycle involves transmission via fresh water and colonization of the renal tubules of their reservoir hosts. Infection of accidental hosts, including humans, may result in life-threatening sequelae. Bacterial outer membrane proteins (OMPs), particularly those with surface-exposed regions, play crucial roles in pathogen virulence mechanisms and adaptation to environmental conditions, including those found in the mammalian host. Therefore, elucidation and characterization of the surface-exposed OMPs of Leptospira spp. is of great interest in the leptospirosis field. A thorough, multi-pronged approach for assessing surface exposure of leptospiral OMPs is essential. Herein, we present evidence for a sub-surface location for most or all of the major leptospiral lipoprotein, LipL32, based on surface immunofluorescence utilizing three different types of antibodies and four different permeabilization methods, as well as surface proteolysis of intact and lysed leptospires. We reevaluate prior evidence presented in support of LipL32 surface-exposure and present a novel perspective on a protein whose location has been misleading researchers, due in large part to its extraordinary abundance in leptospiral cells.

A Cable Laid Is a Cable Played: On the Hibernation Logic behind Urban Infrastructure Mines

Our societies are reliant on metals to such an extent that the total amounts of some of them in the built environment are comparable in size to the remaining amounts in known mountain ores. Because of concerns about mineral scarcity, the United Nations has assessed alternative sources for metal extraction and targeted urban areas in general and infrastructure systems in particular, since these are large, spatially concentrated and rich in metals. Referring to the possibility of recovering these metal stocks, infrastructure systems constitute what material flow researchers has conceptually termed “urban mines.” While most urban infrastructure is in use, significant amounts of cables and pipes have been disconnected and remain in their subsurface locations; they are “hibernating.” In this article, we analyze the occurrence of such hibernation in the Swedish city of Norrköping's urban infrastructure mine where, we know from a previous study, that every fourth kilo of infrastructure is discarded. Our applied perspective is different from the logic of system expansion as a way to meet increased demand often found in the field of infrastructure studies since we are interested in how systems are disconnected and left behind. This enables us to offer a refined understanding of the concepts of infrastructure “decline” and infrastructure “cold spots.” We argue that to prevent the increase of dormant infrastructures and to engage in the urban mining of already dormant infrastructures, we must develop a sensibility to the materiality of derelict infrastructure components and the underlying causes for why they form different kinds of spatial patterns.

The method of lines with numerical differentiation of the sequential temperature–time histories for a facile solution of 1-D inverse heat conduction problems

This work addresses an inverse heat conduction problem (IHCP) in a large planar slab receiving a certain heat flux at one surface while the other surface is thermally insulated. The two different heating conditions to be studied are: (1) constant heat flux and (2) a time-dependent triangular heat flux. For the IHCP, the temperature–time variations at the insulated surface of the large planar slab are obtained with a single temperature sensor. The two temperature–time histories are generated from the solutions of the direct heat conduction problem. The central objective of the paper is to implement the method of lines for the descriptive 1-D heat equation combined with numerical differentiation of: (1) the “measured” temperature–time history at the insulated surface and (2) the temperature–time history at other sub-surface locations. In the end, it is confirmed that excellent predictions of the temperature–time variations at the directly heated surface are obtainable for the two dissimilar heating conditions. This is accomplished with small systems of first-order differential-difference equations, one with two equations and the other with four equations.

The effect of abundant precipitation on coal fire subsidence and its implications in Centralia, PA

Abundant precipitation in 2011 resulted in the formation of nine new sinkholes and many other, smaller subsidence features associated with a coal fire in Centralia, PA. Additionally, fire vent temperatures decreased following prolonged precipitation associated with Hurricane Irene and Tropical Storm Lee. Just over 185-cm of precipitation were measured for central Pennsylvania, which is nearly twice the annual amount and represents the wettest year on record. Precipitation infiltrated the soil and bedrock, and interacted with hot bedrock in the subsurface location of the coal fire. Steam and other gases moved along the pillar structures, through mined-out coal areas, and escaped at the surface exhaust vents along the fire front. Surface regolith and bedrock softened and with the increased water weight, collapsed, producing subsidence features. As a result, sinkholes up to 1.8-m deep and 26-m wide formed. Some of these features have coalesced, forming even larger ellipse-shaped troughs. These subsidence features were mapped along the Bottom, Middle, and Top splits of the Buck Mountain coal from the Llewellyn Formation (middle to upper Pennsylvanian). Aerial thermal infrared images (TIR) reveal the sinkholes and fractures occur in alignment with three thermal anomalies associated with gas and heat release. This may indicate that mined-out coal beds act as conduits for heat circulation or that multiple beds of anthracite coal are on fire in the subsurface in Centralia.

Interpretation of lithogeochemical and geophysical data to identify the buried mineralized area in Cu-Au porphyry of Dalli-Northern Hill

Geochemical and statistical analyses of 165 soil samples led to Cu-Au anomaly separation in Dalli-Northern Hill by using fractal geometry and U-spatial statistic. There was a good correlation between the anomaly areas and outcrops of quartz diorite porphyry (QDP) in the study area. Based on the interpretation of soil data and anomaly areas determination, one trench was suggested in NE-SW direction for follow-up exploration. Based on the rock sample analyses from the trenches in QDP rocks, the ratio of \( \frac{{{\mathrm{Ba}} \times {\mathrm{K}}}}{{{\mathrm{Ca}} \times {\mathrm{Zn}}}} \) clearly separated the mineralization area and considered as an index ratio for follow-up exploration stage. Dalli-Northern Hill anomaly includes pyrite/chalcopyrite/bornite, which is dominantly abundant in the ore body. Three IP profiles (IP04, IP05, and IP06) confirmed the conductivity of the sulfide zone. The background chargeability in the study area was about 5.4 mV/V and the average of maximum apparent chargeability in the study area was 44.4 mV/V, which could be related to the higher intensity of Cu-Fe sulfide minerals. The contact of andesite and quartz diorite has shown the strongest chargeability (71 mV/V) and high magnetic anomalies in the study area. DDH03 and DDH04 boreholes mostly confirmed that the IP/magnetic/geochemical anomalies were related to the contact of intrusive rocks and the wall rock of andesite. The combination of geochemical information from soil and rock together with geophysical data (induced polarization/resistivity) led to the subsurface geological cross sections and location of the mineralized zone enriched of sulfide. The mineralized zone in Dalli-Northern Hill distinct could be identified by potassic to weak sericitic and trace chloritic alteration, high values of the \( \frac{{{\mathrm{Ba}} \times {\mathrm{K}}}}{{{\mathrm{Ca}} \times {\mathrm{Zn}}}} \) ratio accompanied with high gold and copper values and enrichment from magnetite minerals. The high magnetic susceptibility, low resistivity, and high chargeability are considered as geophysical properties of the mineralized zones.

3D seismic imaging of volcanogenic massive sulfide deposits in the Flin Flon mining camp, Canada: Part 1 — Seismic results

A [Formula: see text] 3D-3C seismic survey was conducted within the active Flin Flon mining camp located in Manitoba, Canada. The results for the vertical component data as obtained by conventional dip-moveout and prestack time-migration processing sequences and comparison of images from the 3D seismic volume with the subsurface location of known ore zones and the mine horizon generally showed a very good correlation. A well-defined diffraction response from the shallowest ore zone was observed in the unmigrated data with a corresponding phase reversal in the migrated data at the transition from intact ore to backfilled ore zone. The geometry of unmined and backfilled ore zones compared well with strong reflection amplitudes on corresponding cross sections to depths of [Formula: see text]. At greater depths, the ore zone had a weaker seismic signature due to a combination of effects, including imaging conditions, ore composition, and the increased presence of rhyolite within the mine horizon. In the case of the deeper ore zones that were characterized by low signal-to-noise levels, poststack migration was important in focusing weak ore-related reflections. The 3D data demonstrated the feasibility of detecting and accurately locating ore zones as small as a few million tons to depths of up to 1500 m.

Allocating risk capital for a brownfields redevelopment project under hydrogeological and financial uncertainty

In this study, we defined risk capital as the contingency fee or insurance premium that a brownfields redeveloper needs to set aside from the sale of each house in case they need to repurchase it at a later date because the indoor air has been detrimentally affected by subsurface contamination. The likelihood that indoor air concentrations will exceed a regulatory level subject to subsurface heterogeneity and source zone location uncertainty is simulated by a physics-based hydrogeological model using Monte Carlo realizations, yielding the probability of failure. The cost of failure is the future value of the house indexed to the stochastic US National Housing index. The risk capital is essentially the probability of failure times the cost of failure with a surcharge to compensate the developer against hydrogeological and financial uncertainty, with the surcharge acting as safety loading reflecting the developers' level of risk aversion. We review five methodologies taken from the actuarial and financial literature to price the risk capital for a highly stylized brownfield redevelopment project, with each method specifically adapted to accommodate our notion of the probability of failure. The objective of this paper is to develop an actuarially consistent approach for combining the hydrogeological and financial uncertainty into a contingency fee that the brownfields developer should reserve (i.e. the risk capital) in order to hedge their risk exposure during the project. Results indicate that the price of the risk capital is much more sensitive to hydrogeological rather than financial uncertainty. We use the Capital Asset Pricing Model to estimate the risk-adjusted discount rate to depreciate all costs to present value for the brownfield redevelopment project. A key outcome of this work is that the presentation of our risk capital valuation methodology is sufficiently generalized for application to a wide variety of engineering projects.

Signal-to-noise estimates of time-reverse images

Locating subsurface sources from passive seismic recordings is difficult when attempted with data that have no observable arrivals and/or a low signal-to-noise ratio (S/N). Energy can be focused at its source using time-reversal techniques. However, when a focus cannot be matched to a particular event, it can be difficult to distinguish true focusing from artifacts. Artificial focusing can arise from numerous causes, including noise contamination, acquisition geometry, and velocity model effects. We present a method that reduces the ambiguity of the results by creating an estimate of the (S/N) in the image domain and defining a statistical confidence threshold for features in the images. To do so, time-reverse imaging techniques are implemented on both recorded data and a noise model. In the data domain, the noise model approximates the energy of local noise sources. After imaging, the result also captures the effects of acquisition geometry and the velocity model. The signal image is then divided by the noise image to produce an estimate of the (S/N). The distribution of image (S/N) values due to purely stochastic noise provides a means by which to calculate a confidence threshold. This threshold is used to set the minimum displayed value of images to a statistically significant limit. Two-dimensional synthetic examples show the effectiveness of this technique under varying amounts of noise and despite challenging velocity models. Using this method, we collocate anomalous low-frequency energy content, measured over oil reservoirs in Africa and Europe, with the subsurface location of the productive intervals through 2D and 3D implementations.

Feasibility of Raman microspectroscopic identification of biomarkers through gypsum crystals

The miniaturized Raman spectrometer is considered to be a candidate instrument for the Pasteur payload (the ExoMars mission scheduled for 2018). This mission will, for the first time, combine mobility and access to subsurface locations where organic molecules might be well preserved. Evaporitic crystals are among the potential protected habitats that have been postulated. Various concentrations of biomarkers (beta-carotene, glycine and phthalic acid) dispersed in a gypsum matrix were analyzed through transparent mineral (gypsum) plates of different thicknesses. By doing so, conditions were simulated in which biomarkers were trapped within evaporitic crystals. Using a long-working distance objective, all studied concentrations of biomarkers mixed in gypsum powder were detected. The characteristic Raman bands were easily observable for a 10% mixture of all chosen biomarkers not only through a 3.3 mm plate and but even through a 5.2 mm plate. It was possible to detect key Raman bands of 1% phthalic acid/gypsum mixture and 1% beta-carotene/gypsum mixture even through a 5.2 mm gypsum plate. The 1% beta-carotene/gypsum mixture was still clearly distinguishable through an 8.5 mm gypsum crystal due to the known resonance Raman effect of the molecule.

Ablation of subsurface tumors using an ultra-short pulse laser

This paper demonstrates the novel technique of ablating subsurface tumors with minimal thermal damage to surrounding healthy tissue using a focused laser beam from an ultra-short pulse diode laser source. Experiments were performed on anesthetized healthy mice as well as mice with mammary tumors in order to demonstrate the fundamental advantages of using a focused-beam, ultra-short pulse laser to ablate subcutaneous tissues. The technique was demonstrated through histological analysis of tissue samples after irradiation of anesthetized mice with or without mammary tumors. To demonstrate the efficacy of subsurface focusing, temperature was monitored at the subsurface tumor location and at the surface in an untranslated sample while irradiating with a focused ultra-short pulsed 1552 nm laser. Results show that temperature rise was dramatically greater at the focal depth than at the surface. Irradiation at the subsurface tumor location while translated over time across the tumor location resulted in precise ablation of the tumor. This work shows that a focused-beam ultra-short pulse 1552 nm laser results in precise ablation at the desired location with high efficacy and a minimal zone of collateral thermal and/or mechanical damage.

Accurately Locating a Vertical Magnetic Dipole Buried in a Conducting Earth

The use of a buried vertical magnetic dipole to determine the position of a point inside the Earth is based on the geometric structure of the measured field. A new systematic technique that improves the location accuracy of the surface point in the axis of the buried dipole is developed and tested. It is based on the use of state-of-the-art topographic equipment for the null-field direction measurements, that are further processed by two estimation algorithms, namely, the extended information filter and the extended Kalman filter. In addition, emphasis is placed on the study of the sources of error in order to establish the accuracy of the method. This analysis is conducted in a half-space model in which electromagnetic propagation is studied by numerical integration of analytical solutions. The results are confirmed by a direct solution of the problem by the finite-element method. From the computations, simple equations are provided for practical use. Then, an experimental study shows that the uncertainty of the null-field direction measurements can be modeled by a Gaussian probability density function. In addition, the data of the field experiment are used to validate the proposed subsurface location technique.

The interaction of Cu with Bi nanolines on H-passivated Si(001): an ab initioanalysis

In spite of the known tendency for Cu to be a fast diffuser inside bulk Si, it was recentlyshown that it presents a clear preference for migrating towards a hydrogen terminatedSi(001) surface along the dimer rows; on a surface with Bi nanolines, this will drive the Cutowards the Bi nanolines. In this paper, we present a density functional theory study of thebehaviour of Cu atoms near self-assembled Bi nanolines on the hydrogen-passivated Si(001)surface, predicting that Cu will attack the nanolines and insert in the Bi–Si bonds. Themigration routes from subsurface locations and surface deposition are found and thepairing tendency for Cu is examined and compared to that for Ag on Bi nanolines.

Observational constraints on the ultrahigh energy cosmic neutrino flux from the second flight of the ANITA experiment

The Antarctic Impulsive Transient Antenna (ANITA) completed its second long-duration balloon flight in January 2009, with 31 days aloft (28.5 live days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov emission from 200 to 1200 MHz, arising from the Askaryan charge excess in ultra-high energy neutrino-induced cascades within Antarctic ice. This flight included significant improvements over the first flight in the payload sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of in-flight calibration pulses from surface and sub-surface locations verifies the expected sensitivity. In a blind analysis, we find 2 surviving events on a background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest limit to date for 1-1000 EeV cosmic neutrinos, excluding several current cosmogenic neutrino models.

Atomic-Scale Geometry and Electronic Structure of Catalytically Important Pd/Au Alloys

Pd/Au bimetallic alloys catalyze many important reactions ranging from the synthesis of vinyl acetate and hydrogen peroxide to the oxidation of carbon monoxide and trimerization of acetylene. It is known that the atomic-scale geometry of these alloys can dramatically affect both their reactivity and selectivity. However, there is a distinct lack of experimental characterization and quantification of ligand and ensemble effects in this system. Low-temperature, ultrahigh vacuum scanning tunneling microscopy is used to investigate the atomic-scale geometry of Pd/Au111 near-surface alloys and to spectroscopically probe their local electronic structure. The results reveal that the herringbone reconstruction of Au111 provides entry sites for the incorporation of Pd atoms in the Au surface and that the degree of mixing is dictated by the surface temperature. At catalytically relevant temperatures the distribution of low coverages of Pd in the alloy is random, except for a lack of nearest neighbor pairs in both the surface and subsurface sites. Scanning tunneling spectroscopy is used to examine the electronic structure of the individual Pd atoms in surface and subsurface sites. This work reveals that in both surface and subsurface locations, Pd atoms display a very similar electronic structure to the surrounding Au atoms. However, individual surface and subsurface Pd atoms are depleted of charge in a very narrow region at the band edge of the Au surface state. dI/dV images of the phenomena demonstrate the spatial extent of this electronic perturbation.

Ray-based stochastic inversion of prestack seismic data for improved reservoir characterization

Trace inversion for reservoir parameters is affected by angle averaging of seismic data and wavelet distortion on the migration image. In an alternative approach to stochastic trace inversion, the data are inverted prestack before migration using 3D dynamic ray tracing. This choice makes it possible to interweave trace inversion with Kirchhoff migration. The new method, called ray-based stochastic inversion, is a generalization of current amplitude versus offset/amplitude versus angle (AVO/AVA) inversion techniques. The new method outperforms standard stochastic inversion techniques in cases of reservoir parameter estimation in a structurally complex subsurface with substantial lateral velocity variations and significant reflector dips. A simplification of the method inverts the normal-incidence response from reservoirs with approximately planar layering at the subsurface target locations selected for inversion. It operates along raypaths perpendicular to the reflectors, the direction that offers optimal resolution to discern layering in a reservoir. In a test on field data from the Gulf of Mexico, reservoir parameter estimates obtained with the simplified method, the estimates found by conventional stochastic inversion, and the actual values at a well drilled after the inversion are compared. Although the new method uses only 2% of the prestack data, the result indicates it improves accuracy on the dipping part of the reservoir, where conventional stochastic inversion suffers from wavelet stretch caused by migration.

ERC-group microflex: microbiology of Dehalococcoides-like Chloroflexi

The Microflex project, funded within the first call of the European Research Council, focuses on a specific group of bacteria, the Dehalococcoides-like Chloroflexi. This group of bacteria deeply rooting in the phylogenetic tree is formed by several cultivated strains of the proposed genus “Dehalococcoides” and many sequences of uncultivated organisms mostly from marine sediments or terrestrial subsurface locations. The project compares cultivated Dehalococcoides species growing by organohalide respiration using halogenated compounds as electron acceptors with marine Chloroflexi populations. For this comparison a wide array of different approaches and techniques are used including cultivation, biochemical analyses, molecular tools and isotopic fractionation measurements. The project aims at contributing to the understanding of the physiology of Dehalococcoides-like Chloroflexi in deep marine sediments and their mode of living. A second aim of the project is the further understanding of the physiology and biochemistry of dehalogenating Dehalococcoides species and how these bacteria can be used efficiently for bioremediation of contaminated subsurface environments.

Structural evolution of sulfur overlayers on Pd(1 1 1)

Low energy ion scattering spectroscopy (LEISS) has been used to characterize the evolution of ordered structures of S on the Pd(1 1 1) surface during annealing. During exposure of the Pd(1 1 1) surface to 0.7 L H 2S at 300 K—conditions that produce the S(√3 × √3)R30 overlayer—the intensity of the Pd LEIS signal decreases and a feature assigned to adsorbed S appears as the adsorbed layer forms. When the surface is held at 300 K after exposure to H 2S is stopped, the LEIS Pd intensity partially recovers and the S signal weakens, presumably as surface S atoms assume their equilibrium positions in the S(√3 × √3)R30 overlayer. Subsequent annealing of the S(√3 × √3)R30 structure at 700 K causes it to convert into a S(√7 × √7)R19 overlayer, whose LEIS spectrum is identical to that of clean Pd(1 1 1). The absence of LEIS evidence for S atoms at the exposed surface of the S(√7 × √7)R19 overlayer is at odds with published models of a mixed Pd–S top layer. Despite the similarity of the LEIS spectra of Pd(1 1 1) and Pd(1 1 1)–S(√7 × √7)R19, their activities for dissociative hydrogen adsorption are very different—the former readily adsorbs hydrogen at 100 K, while the latter does not—suggesting that S exerts its influence on surface chemistry from subsurface locations.

Turbulent Channel Flows on a Rotating Earth

Abstract This paper deals with flow in a rectilinear channel on a rotating earth. The flow is directed perpendicular to the background planetary vorticity; both an analytical theory and numerical simulations are employed. The analytical approach assumes the existence of an eddy viscosity and employs a perturbation expansion in powers of the reciprocal of the Rossby number (Ro). At lowest order, a cross-channel circulation arises because of the tilting of the planetary vorticity vector by the shear in the along-channel direction. This circulation causes a surface convergence, which achieves its maximum value at a channel aspect ratio (= width/depth) of approximately 10. The location of the maximum surface convergence moves from near the center of the channel to a position very near the sidewalls as the aspect ratio increases from O(1) to O(100). To include the effects of turbulence, direct numerical pseudospectral simulations of the equations of motion are employed. While holding the friction Reynolds number fixed at 230.27, a series of simulations with increasing rotation (Ro = ∞, 10, 1.0, 0.1) are performed. The channelwide circulation cell observed in the analytical theory occurs for the finite Rossby number, but is displaced by lateral self-advection. In addition, turbulence-driven corner circulations appear, which make the along-channel maximum velocity appear at a subsurface location. The most interesting effect is the segregation of the turbulence to one side of the channel, while the turbulence is suppressed on the opposite side.

CO2 storage capacity calculations for the Dutch subsurface

Estimating the capacity of a geological formation to store CO2 is not a straightforward or simple process. Bradshaw [1] has recently listed various estimations for both regional and global CO2 storage capacity. The estimations were quoted as very large with ranges for the estimates in the order of 100 s to 10,000 s Gt of CO2. Clearly this work shows the lack of definitions, rules and general practices in calculating CO2 storage potential. In earlier studies TNO has strongly emphasised the need for a more uniform and standard method to calculate the storage potential of any subsurface location, either a partial or empty hydrocarbon field or aquifer. TNO prefers to consider in any storage capacity calculation the inclusion of a concept of total affect space, i.e. all space that has its state or qualities changed by the storage operation over the total storage time. Furthermore, we will have to consider the injectivity of the selected injection location and the pressure and fluid conductivity of the total affected storage space. In addition, the intended free CO2 storage location will need to have enough storage space or enough sealing capacity to contain the CO2 for at least 10,000 years and prevent it from migrating to the surface. TNO has developed a method (van der Meer, [4]) which has been used for calculating of the maximum storage volume in the Netherlands. The method is based on the affected space and maximum pressurisation. The storage potential is further based on injectivity and finally the storage efficiency of the geological trap. The results of this work are compared with previous estimations. © 2009 Elsevier Ltd. All rights reserved.