Application Of Seismic Methods Research Articles

Seismic Advances in Process Geomorphology

One of the pillars of geomorphology is the study of geomorphic processes and their drivers, dynamics, and impacts. Like all activity that transfers energy to Earth's surface, a wide range of geomorphic process types create seismic waves that can be measured with standard seismic instruments. Seismic signals provide continuous high-resolution coverage with a spatial footprint that can vary from local to global, and in recent years, efforts to exploit these signals for information about surface processes have increased dramatically, coalescing into the emerging field of environmental seismology. The application of seismic methods has the potential to drive advances in our understanding of the occurrence, timing, and triggering of geomorphic events, the dynamics of geomorphic processes, fluvial bedload transport, and integrative geomorphic system monitoring. As new seismic applications move from development to proof of concept to routine application, integration between geomorphologists and seismologists is key for continued progress. ▪ Geomorphic activity on Earth's surface produces seismic signals that can be measured with standard seismic instruments. ▪ Seismic methods are driving advances in our understanding of the occurrence, triggering, and internal dynamics of a range of geomorphic processes. ▪ Dedicated seismic-based observatories offer the potential to comprehensively characterize geomorphic activity and its impacts across a landscape. ▪ Collaboration between seismologists and geomorphologists is fostering the development of new applications, models, and analysis techniques for geomorphic seismology.

Seismic profile solution under conditions of thawing permafrost with technogenic depression

The article given presents the results of geophysical research of the certain types of geodynamical phenomenon, which is generally located on areas with permafrost soil layers. The detailed description to the research methods of refracting interface of the technogenic thawing ground area under the conditions of flooded pressure by refraction and reflection methods is given. Setting of the problem and detection of the nature of the changes in the properties and configuration of the permafrost and thawed soil layers in the grounds of embankment is practically solved by the integrated application of seismic methods that in theory have different kinematics due to propagation of elastic waves and methods of interpretation the seismic profile.

Estimating picking errors in near‐surface seismic data to enable their time‐lapse interpretation of hydrosystems

ABSTRACTTime‐lapse applications of seismic methods have been recently suggested in the near‐surface scale to track hydrological properties variations due to climate, water level changes, or permafrost thaw, for instance. But when it comes to traveltime tomography or surface‐wave dispersion inversion, a careful estimation of the data variability associated with the picking process must be considered prior to any time‐lapse interpretation. In this study, we propose to estimate picking errors that are due to the inherent subjectivity of human operators, using statistical analysis based on picking repeatability. Two seismic datasets were collected along the same profile under distinct hydrological conditions across a granite–micaschist contact at the Ploemeur hydrological observatory (France). Both datasets were recorded using identical equipment and acquisition parameters. A thorough statistical analysis is conducted to estimate picking uncertainties, at the 99% confidence level, for both P‐wave first arrival time and surface‐wave phase velocity. With the suggested workflow, we are able to identify 33% of the P‐wave traveltimes and 16% of the surface‐wave dispersion data, which can be considered significant enough for time‐lapse interpretations. In this selected portion of the data, point‐by‐point differences highlight important variations linked to different hydrogeological properties of the subsurface. These variations show strong contrasts with a non‐monotonous behaviour along the line, offering new insights to better constrain the dynamics of this hydrosystem.

Feasibility of using passive seismic diffractions for imaging and monitoring

SUMMARY We present a feasibility study of using passive seismic data for imaging of diffractors. Imaging and characterisation of seismic diffractors is important for many applications of seismic methods, including carbon geosequestration, since in sedimentary setting the diffractors are associated with terminations of layers at faults, as well as edges of the zones altered through the reservoir depletion or fluid (e.g. CO2) injection. One of the findings is that the diffracted waves from ambient sources can be sometimes incorrectly interpreted as active seismic sources that might lead to wrong conclusions about induced seismicity of processes generating the ambient noise, such as injection of fluids in the subsurface.

Applications of shallow-seismic exploration methods for mechanical characterization of soil and rock bodies at engineering project sites in Colombia

The application of seismic methods for rock and soil-mass characterization has proved to be useful for engineering projects of any kind. These methods can predict the presence and geometry of low-competent subsoil materials and can define preliminary structural designs for each project. In three studies in Colombia, refraction tomography and multichannel analysis of surface waves (MASW) were applied for road tunnels and multistory building construction, respectively. In situ rock and soil types were classified based on P- and S-wave measurements, and preliminary structural designs and construction methods were recommended for each case. Both rock and soil classifications and preliminary structural designs must be refined with direct subsoil-characterization methods such as core drilling and laboratory testing.

Targeting nickel sulfide deposits from 3D seismicreflection data at Kambalda, Australia

The greenstone belts of the Yilgarn Craton, Western Australia, host numerous Archaean gold, nickel, and iron ore deposits. These deposits typically are found in complex geologic structures hidden by a deep, heterogeneous, and often conductive regolith profile. This added complexity limits the depth of penetration for the potential field methods, but at the same time opens new revenue possibilities through the application of seismic methods. To explore this opportunity, we acquired high-resolution, experimental, 3D seismic data over Lake Lefroy in Kambalda, Western Australia. The main objective was to map exceptionally complex, deep structures associated with Kambalda dome. Survey design used 3D ray tracing to improve the distribution of the common reflection points across ultramafic-basalt contacts which host numerous small, high-grade nickel sulfide deposits. A combination of small explosive sources, high-shot/receiver density, and exceptionally good coupling over the ultrasalty lake surface produced seismic data of very high quality. Processing focused on computation of accurate static and dynamic corrections, whereas imaging was helped by the existing geologic model. Advanced volumetric interpretation supported by seismic forward modeling was used to guide mapping of the main lithological interfaces and structures. Forward modeling was carried out using rock properties obtained from ultrasonic measurements and one borehole, drilled in the proximity of the 3D seismic volume. Using this information, geometric constraints based on the typical size of ore bodies found in this mine and a simple window-based seismic attribute, several new targets were proposed. Three of these targets subsequently have been drilled and new zones of mineralization were intercepted. The case study presented demonstrates that high-quality, high-resolution, 3D seismic data combined with volumetric seismic interpretation could become a primary methodology for exploration of deep, small, massive sulfide deposits distributed across the Kambalda area.

Seismic processing, inversion, and AVO for gold exploration — Case study from Western Australia

We investigate the potential of using high-resolution seismic methods for rock characterization and for targeting of gold deposits at the St. Ives gold camp. The application of seismic methods in hard-rock environments is challenged by complex structures, intrinsically low signal-to-noise ratio, regolith distortions, and access restrictions. If these issues can be addressed, then the unparalleled resolving power of reflection seismic can be used for mineral exploration. Appropriate spatial sampling of the wavefield combined with a survey geometry design and rigorous data processing to incorporate high fold and long offsets are necessary for creation of high-quality seismic images. In the hard-rock environment of Western Australia, accurate static corrections and multiphase velocity analysis are essential processing steps. This is followed by a rigorous quality control following each processing step. In such a case, we show that the role of reflection seismic could be lifted from mere identification of first-order structures to refined lithological analyses. Five deep boreholes with sonic logs and core sample test data were used to calibrate 2D seismic images. Despite seismic images were produced with relatively robust scaling it was possible to achieve reasonably high seismic-log correlation across three of the tightly spaced boreholes using a single composite wavelet. Amplitude-versus-offset (AVO) analysis indicated that gold-bearing structures may be related to elevated AVO effect and increased reflectivity. Consequently, partial stack analysis and acoustic and elastic inversions were conducted. These results and impedance crossplots were then evaluated against known gold occurrences. While still in the preliminary stages, hard-rock seismic imaging, inversion, and the application of AVO techniques indicated significant potential for targeting mineral reserves.

Analysis of the symmetry of a stressed medium using nonlinear elasticity

Velocity variations caused by subsurface stress changes play an important role in monitoring compacting reservoirs and in several other applications of seismic methods. A general way to describe stress- or strain-induced velocity fields is by employing the theory of nonlinear elasticity, which operates with third-order elastic (TOE) tensors. These sixth-rank strain-sensitivity tensors, however, are difficult to manipulate because of the large number of terms involved in the algebraic operations. Thus, even evaluation of the anisotropic symmetry of a medium under stress/strain proves to be a challenging task. We employ a matrix representation of TOE tensors that allows computation of strain-related stiffness perturbations from a linear combination of [Formula: see text] matrices scaled by the components of the strain tensor. In addition to streamlining the numerical algorithm, this approach helps to predict strain-induced symmetry using relatively straightforward algebraic considerations. For example, our analysis shows that a transversely isotropic (TI) medium acquires orthorhombic symmetry if one of the principal directions of the strain tensor is aligned with the symmetry axis. Otherwise, the strained TI medium can become monoclinic or even triclinic.

Seismic Imaging: Science and Art

Seismic imaging is a process of geophysical inversion and consists of data acquisition, processing and interpretation. Errors introduced in any of these stages can have a serious impact on later stages and the final results. The processing stage probably has the greatest scope for error. Modern processing packages allow considerable freedom in the selection of processing algorithms and parameters. Even if essentially the same processing/work flow is followed, different results may be obtained from different data processors. End-users of the data can be unwittingly placed in a very difficult position. The seismic method itself is firmly based on the theory of elastic wave propagation. However the data processing and interpretation stages can be viewed as requiring the application of scientific art based on experience, a thorough understanding of the data in question, the field parameters, the options available for processing and the geological setting. This is not a new observation or theme, but in the light of recent experience in the application of seismic methods in mining, we revisit it in this paper. We use real data examples to illustrate the non-uniqueness of seismic data processing and the consequences of choosing different processing algorithms and parameters. The objective of this paper is to provide an awareness to some important issues in the contemporary use of seismic surveying in the hope that through this, better and more reliable results can be delivered and exploited by the end-users.

2-D velocity structure of the buried ancient canal of Xerxes: an application of seismic methods in archaeology

An ancient buried canal whose existence had been disputed even in antiquity has been detected and described by the modern seismic methods of geophysics. Its dimensions concur with those described by the ancient historian, Herodotus. The 2-km long canal is located in the Chalkidiki peninsula in northern Greece, and was constructed some 2500 years ago by the Persian King Xerxes. Beyond the classical processing of the seismic data, inverse seismic modeling was also implemented, giving an improved and more complete picture. The inverse modeling tested the validity of the results of the seismic refraction and reflection seismics and provided 2-D velocity structure profiles. Over much of the isthmus, it was possible to trace the route of the ancient canal by connecting the deepest points of all the sections.

Surface and borehole seismic methods to delineate kimberlite pipes in Australia

Gravity, magnetic, and electromagnetic methods are primary exploration techniques used in kimberlite exploration to define a kimberlite pipe's location and shape. Sometimes these methods produce nonunique results because of weathering of the upper part of a kimberlite pipe and its considerable inhomogeneity. Complex pipe geometries and associated faulting and fracturing may be very difficult to assess by potential-field methods. Application of seismic methods in kimberlite exploration has been limited. In sedimentary basins, however, kimberlite pipes are likely to be a suitable target for the application of seismic reflection methods because of the difference in elastic properties between the pipe material and the host rock. The drawback of surface seismic methods is that they are not designed for direct detection of vertical bodies such as a pipe. However, a kimberlite pipe may be inferred from seismic data indirectly by observing the termination of reflections against its flanks. Such an approach can produce good results if the sedimentary sequence is of moderate to high reflectivity. Unfortunately, McArthur Basin sediments of the Northern Territory in Australia are quite poor reflectors (Figure 1). The only reflecting horizon would probably be the sandstone/black shale interface at 140 m. Near-surface conditions are also unfavorable for surface seismic because of a thick layer of bull dust, which causes poor geophone coupling. Hence, very poor seismic data quality is typical for this area. In this study, instead of attempting a conventional surface seismic reflection approach, we used modes generated by a kimberlite pipe to precisely determine its location. The single borehole imaging (SBI) method also was used for delineation of the kimberlite pipe shape at depth. By a combined analysis of P - and S -wave data recorded on the surface and in downhole experiments, the pipe's location, shape, …

A review of high-resolution seismic profiling across the Sudbury, Selbaie, Noranda, and Matagami mining camps

Lithoprobe high-resolution seismic surveys have provided the first systematic images of the deep stratigraphy in four major Canadian mining camps (Noranda, Matagami, Sudbury, and Selbaie). Systematic compressional wave velocity and density measurements in deep boreholes have established that lithological contacts were the main impedance contrast imaged, although reflections from faults and deformation zones have also been observed. The strongest reflections are attributed to mafic intrusions and some sulphides and oxides. Integrating seismic, physical rock property measurements, and geological data has resulted in the revision of several geological models with direct impact on local strategies for deep mineral exploration. Mining companies have shown an interest in seismic reflection methods and this has led to several follow-up studies. The application of seismic methods to the direct detection of massive sulphides, based on physical rock property measurements, has been studied through two-dimensional and three-dimensional (3D) seismic imaging and vertical seismic profiling technologies. The challenge will now be to optimize 3D seismic imaging for mineral exploration and to improve seismic data processing by enhancing the seismic response from deep, lenticular orebodies.

Ultrasonic Crosshole Assessment of Fracture Density and Stress Variations in Crystalline Rock

The potential for application of seismic methods in the evaluation and monitoring of nuclear waste repositories is immense. Past field studies have established that variations in velocity and attenuation indicate changes in the fracture density of the rock mass surrounding a storage facility. A study was undertaken to determine the effects upon velocity and attenuation of varying stress fields surrounding a crystalline repository. Laboratory experiments performed on fractured core samples found that amplitude and rise time are sensitive to stress applied parallel to travel path and velocity is not. Ultrasonic crosshole measurements were taken within the rock mass surrounding an underground research facility. The crosshole method was able to detect a zone of high fracture density caused by blasting near the surface of the room. The blast damage zone was characterized by relatively low velocities and amplitudes and large rise times. Moving outward into the rock mass, velocity stabilized while amplitude and rise time varied significantly indicating the existence of a stress concentration. This coincides well with the estimated stress distribution based on measured in situ stresses. Other significant variations in acoustic parameters were encountered and attributed to changes in fracture densities.

Fundamentals of the Seismic Method

The similarity between the laws governing light transmission and shockwave propagation can be used to advantage to demonstrate the problems which are associated with correct interpretation and application of seismic methods. When used in the right context refraction seismic applications for foundation engineering constitute nondestructive in situ testing of the ground material. Recognition of this feature enables the engineer to use obtained results in a wider perspective.