Geophysics
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Cascaded f-k migration: Removing the restrictions on depth‐varying velocity Stolt’s frequency‐wavenumber (f-k) method is computationally efficient and has unlimited dip accuracy for constant‐velocity media. Although the f-k method can handle moderate vertical velocity variations, errors become unacceptable for steep dips when such variations are large. This paper describes an extension to the f-k method that removes its restrictions on vertical velocity variation... ... hiện toàn bộ
Geophysics - Tập 53 Số 7 - Trang 881-893 - 1988
Shallow-structure characterization by 2D elastic full-waveform inversion Assessing the effectiveness of elastic full-waveform-inversion (FWI) algorithms when applied to shallow 2D structures in the presence of a complex topography is critically important. By using FWI, we overcome inherent limitations of conventional seismic methods used for near-surface prospecting (acoustic tomography and multichannel spectral analysis of surface waves). The elastic forward ... ... hiện toàn bộ
Geophysics - Tập 76 Số 3 - Trang R81-R93 - 2011
A passive seismic survey over a gas field: Analysis of low-frequency anomaliesPassive seismic low-frequency (from approximately [Formula: see text]) data have been acquired at several locations around the world. Spectra calculated from these data, acquired over fields with known hydrocarbon accumulations, show common spectral anomalies. Verification of whether these anomalies are common to only a few, many, or all hydrocarbon reservoirs can be provided only if more ... ... hiện toàn bộ
Geophysics - Tập 74 Số 2 - Trang O29-O40 - 2009
Sinkhole detection with 3D full seismic waveform tomography Sinkhole collapse may result in significant property damage and even loss of life. Early detection of sinkhole attributes (buried voids, raveling zones) is critical to limit the cost of remediation. One of the most promising ways to obtain subsurface imaging is 3D seismic full-waveform inversion. For demonstration, a recently developed 3D Gauss-Newton full-waveform inversion (3D GN-FWI) m... ... hiện toàn bộ
Geophysics - Tập 85 Số 5 - Trang B169-B179 - 2020
3D crosshole ERT for aquifer characterization and monitoring of infiltrating river water The hydrogeological properties and responses of a productive aquifer in northeastern Switzerland are investigated. For this purpose, 3D crosshole electrical resistivity tomography (ERT) is used to define the main lithological structures within the aquifer (through static inversion) and to monitor the water infiltration from an adjacent river. During precipitation events and subsequent riv... ... hiện toàn bộ
Geophysics - Tập 76 Số 2 - Trang G49-G59 - 2011
Inversion of fracture density from field seismic velocities using artificial neural networksThe inversion of fracture density from field measured P- and S-wave seismic velocities is performed using a neural network trained with an output from the modified displacement discontinuity fracture model. The basic idea is to use input‐output pairs generated by the fracture model to train the neural network. Once the neural network is trained, inversion of fracture density from field‐mea... ... hiện toàn bộ
Geophysics - Tập 63 Số 2 - Trang 534-545 - 1998
AMBIGUITY IN GEOPHYSICAL INTERPRETATION The question of uniqueness or otherwise of the various geophysical methods has been looked into from a general point of view. A method is theoretically determinate or indeterminate according as the totality of unknowns is smaller or greater than that of the independent measurables. While all natural field methods fall in the latter category, all applied field methods do not necessarily co... ... hiện toàn bộ
Geophysics - Tập 27 Số 1 - Trang 90-99 - 1962
Nonlinear refraction traveltime tomographyA few important issues for performing nonlinear refraction traveltime tomography have been identified. They include the accuracy of the traveltime and raypath calculations for refraction, the physical information in the refraction traveltime curves, and the characteristics of the refraction traveltime errors. Consequently, we develop a shortest path ray‐tracing method with an optimized nod... ... hiện toàn bộ
Geophysics - Tập 63 Số 5 - Trang 1726-1737 - 1998
Improved hydrogeophysical imaging by structural coupling of 2D magnetic resonance and electrical resistivity tomography Describing hydraulic properties in the subsurface in at least two dimensions is one of the main objectives in hydrogeophysics. However, due to the limited resolution and ambiguity of the individual methods, those images are often blurry. We have developed a methodology to combine two measuring methods, magnetic resonance tomography (MRT) and electrical resistivity tomography (ERT). To thi... ... hiện toàn bộ
Geophysics - Tập 86 Số 5 - Trang WB77-WB88 - 2021
Magnetic resonance tomography constrained by ground-penetrating radar for improved hydrogeophysical characterization Geophysical methods can characterize aquifer systems noninvasively and are particularly helpful to image the complex depositional architecture of the subsurface. Among these, ground-penetrating radar (GPR) is an effective tool for detailed investigations of shallow subsurface geometry, but it provides only limited information on hydraulic properties. Magnetic resonance tomography (MRT) pr... ... hiện toàn bộ
Geophysics - Tập 85 Số 6 - Trang JM13-JM26 - 2020
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