Publications
197 results found
Ratcliffe A, Win C, Vinje V, et al., 2011, Full waveform inversion: A North Sea OBC case study, SEG Technical Program Expanded Abstracts, Vol: 30, Pages: 2384-2388, ISSN: 1052-3812
Full Waveform Inversion (FWI) aims to obtain superior velocity models by minimizing the difference between observed and modelled seismic waveforms. We apply FWI to a North Sea OBC field data set with wide azimuths and more than 10 km long offsets. We discuss the methodology used and the associated practical issues. Our FWI result has revealed detailed velocity features associated with thin, gas-charged layers and faulting in the shallow sections of the model. We demonstrate that this velocity update has improved the imaging of the deeper structures. © 2011 Society of Exploration Geophysicists.
Yaeger P, So RJ, Albanese D, et al., 2011, Editor's column: The library walk, PMLA, Vol: 126, Pages: 9-37, ISSN: 0030-8129
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- Citations: 1
Ratcliffe A, Win C, Vinje V, et al., 2011, Full waveform inversion: A North Sea OBC case study, Pages: 2384-2388
Full Waveform Inversion (FWI) aims to obtain superior velocity models by minimizing the difference between observed and modelled seismic waveforms. We apply FWI to a North Sea OBC field data set with wide azimuths and more than 10 km long offsets. We discuss the methodology used and the associated practical issues. Our FWI result has revealed detailed velocity features associated with thin, gas-charged layers and faulting in the shallow sections of the model. We demonstrate that this velocity update has improved the imaging of the deeper structures.
Morgan JV, Warner MR, Collins GS, et al., 2011, Full waveform tomographic images of the peak ring at the Chicxulub impact crater, Journal of Geophysical Research, Vol: 116
Peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation. The precise lithology and kinematics of peak ring formation, however, remains unclear. Previous work has revealed a suite of bright inward-dipping reflectors beneath the peak ring at the Chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity. New 2D full-waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin (~100-200 m thick) layer of low-velocity (~3000-3200 m/s) rocks. This low-velocity layer is most likely to be composed of highly porous, allogenic impact breccias. Our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors. Across the peak ring, velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation, where the rocks that form the peak ring originate from uplifted basement that has been subjected to high shock pressures (10-50 GPa), and lie above downthrown sedimentary rocks that have been subjected to shock pressures of < 5 GPa. These observations suggest that low-velocities within the peak ring may be related to shock effects and that the dipping reflectors underneath the peak ring might represent the boundary between highly-shocked basement and weakly-shocked sediments.
Cobden LJ, Tong CH, Warner MR, 2010, INFLUENCE OF ACOUSTIC SOURCE DENSITY ON CROSS-CORRELATED SIGNALS: IMPLICATIONS FOR AMPLITUDE-BASED TOMOGRAPHY IN HELIOSEISMOLOGY, ASTROPHYSICAL JOURNAL, Vol: 725, Pages: 313-318, ISSN: 0004-637X
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- Citations: 2
Shah N, Warner M, Guasch L, et al., 2010, Waveform inversion of surface seismic data without the need for low frequencies, SEG
Barton PJ, RAF G, Morgan JV, et al., 2010, Seismic images of Chicxulub impact melt sheet and comparison with the Sudbury structure, Large Meteorite Impacts and Planetary Evolution IV, Editors: Reimold, Gibson, Publisher: Geological Society of America, Pages: 103-114, ISBN: 9780813724652
Da Silva NV, MacGregor L, Morgan J, et al., 2010, A domain decomposition method for 3-D controlled source electromagnetics, Pages: 660-664
Three dimensional controlled source electromagnetics (CSEM) forward modelling in the frequency domain requires the solution of a large scale, complex and linear system. Such a system when derived from finite elements and finite differences formulations is sparse and ill-conditioned. The use of direct solvers is prohibitively expensive for realistic-sized problems since several million degrees of freedom are usually involved. To avoid inherent hardware limitations iterative solvers are an option, however their potential efficiency relies on the use of efficient pre-conditioning. We present an alternative pre-conditioner for the CSEM forward modelling problem, based on the Schur complement method, and will discuss some limitations and possible solutions.
Guasch L, Stekl I, Umpleby A, et al., 2010, 3D elastic wavefield tomography in the time domain, Pages: 4390-4394
Wavefield inversion tries to minimise the difference between real and modelled seismic data, which means that its success relies in the accuracy of the wave equation solver used in the process. Then, the wave equation solver should take elastic phenomena into account in order to compare its results with real field data. The purpose of our project was to develop a 3D wavefield tomography algorithm with an elastic wave equation solver in order to recover elastic properties. First formulations of the elastic inverse problem were published more than 20 years ago (Tarantola (1986); Mora (1987)), but only recently the computational resources needed to apply it to 3D have become available.
Morgan J, Christeson G, Warner M, 2010, Deep ocean 3D tomography on field data, Pages: 232-236
We have run a suite of 2D and 3D wavefield inversions to recover fine-scale velocity structure in upper oceanic crust. The data were acquired on a plateau, close to a transform fault in deep water in the Pacific ocean. At the fault, a vertical section of oceanic crust is exposed and has been mapped using submersibles, hence our inverted velocity models can be directly compared with adjacent outcrop data. Synthetic tests using the 2D inversion code suggest that the inverted velocity structure may contain artefacts caused by offline arrivals and feathering of the streamer. Synthetic tests using the 3D inversion code show that true velocity structure can be recovered, and 3D inversions of the real data suggest that there is a velocity inversion in the upper oceanic crust in the area modelled.
Guasch L, Stekl I, Umpleby A, et al., 2010, Elastic wavefield inversion in three dimensions, 72nd European Association of Geoscientists and Engineers Conference and Exhibition Incorporating SPE EUROPEC 2010, Workshops, Pages: 212-215
Warner M, Umpleby A, Stekl I, et al., 2010, 3D full-wavefïeld tomography: Imaging beneath heterogeneous overburden, 72nd European Association of Geoscientists and Engineers Conference and Exhibition Incorporating SPE EUROPEC 2010, Workshops, Pages: 298-302
We have developed computer codes and work-flows for 3D acoustic waveform inversion in both the frequency and time domains. We have applied these methods to several 3D field datasets with a variety of acquisition geometries and target depths. In each case, wavefield tomography was able to obtain a high-resolution high-fidelity velocity model of the heterogeneous overburden, and consequently to improve subsequent depth imaging of an underlying target.
Stekl I, Umpleby A, Warner M, 2010, Seismic anisotropy effects in 3D wavefield tomography, 72nd European Association of Geoscientists and Engineers Conference and Exhibition Incorporating SPE EUROPEC 2010, Workshops, Pages: 278-282
We are presenting results how seismic anisotropy may affect waveform inversion images. Result from our Marmousi model extended to 3D as 2.5D morel show that not including appropriate anisotropy in the modelling algorithm can lead to mispositioning of anomalies in the images.
Shah NK, Warner MR, Guasch L, et al., 2010, Waveform inversion from a poor starting model - Using a residual ’drip-feed’ strategy, 72nd European Association of Geoscientists and Engineers Conference and Exhibition Incorporating SPE EUROPEC 2010, Workshops, Pages: 261-265
We present a new waveform inversion scheme designed to avert the need for an accurate starting model and low frequency content in the data - a necessary key step for realising the potential of the technique in a wider range of practical applications than currently possible. The scheme operates by preceding the inversion of the field data by inversion of intermediate datasets - synthesised from the unwrapped phase-residuals at the lowest useable frequency. We demonstrate its effectiveness over the corresponding conventional approach in a synthetic inversion of the Marmousi dataset with a minimum frequency of 5Hz.
Umpleby A, Warner M, Stekl I, 2010, Time vs frequency for 3D wavefield tomography, 72nd European Association of Geoscientists and Engineers Conference and Exhibition Incorporating SPE EUROPEC 2010, Workshops, Pages: 283-287
Unlike the situation in two-dimensions, where direct factorisation of the matrix equations makes frequency-domain methods much faster than explicit solution in the time-domain, the computational resources required for practical wavefield tomography in 3D can be rather similar in the two domains. We have developed and optimised schemes that undertake wavefield tomography using explicit time stepping in the time domain and that iteratively solve the matrix equations of the implicit problem in the frequency domain. We have applied these two methods systematically to the same suite of problems. In the frequency domain, the principal advantages are that the initial tomographic updates for lowest frequencies are often seen more quickly, and spatial resolution can be better at the highest frequencies. In the time domain, one of the principal advantages is that it is possible to mute and/or weight the field data in time, and consequently the method can be made to work more effectively with difficult datasets. In practice, both approaches are useful, and both should be available within a comprehensive suite of inversion tools.
Guasch L, Warner MR, Stekl I, et al., 2010, 3D elastic wavefield inversion in the time domain, 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010, Vol: 1, Pages: 26-30
We have developed a 3D tomographic wavefield inversion code that solves the fully elastic wave equation in the time domain using finite differences. We show results of applying this elastic code to different synthetic 3D problems. © 2010, European Association of Geoscientists and Engineers.
Shah NK, Warner MR, Guasch L, et al., 2010, A strategy for waveform inversion without an accurate starting model, 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010, Vol: 7, Pages: 4846-4850
A key limitation of waveform inversion as currently implemented is the need for a starting model of high accuracy or field data with low frequencies. Here we present a new approach - staged waveform inversion - designed to mitigate this need and thereby permit the application of waveform inversion to a much wider range of datasets. © 2010, European Association of Geoscientists and Engineers.
Silva NVD, Morgan J, MacGregor L, et al., 2009, An approach for multisource 3-D marine CSEM modelling in the frequency-domain, SEG Technical Program Expanded Abstracts, Vol: 28, Pages: 883-887, ISSN: 1052-3812
Summary: Geophysical multi-source electromagnetic modelling is usually performed solving a linear system of equations for each right-hand side. This approach can be prohibitively expensive when the system of equations has a large number of degrees of fredom and sources. We present an alternative method for multi-source forward modelling of marine CSEM data. For the discretization of the electric field equation we use edge finite elements which naturally satisfy the material interface conditions for the electric field and avoid the presence of spurious modes in the solution. For solving the system of equations we use the software package MUMPS to factorize the system of equations. A solution for each right-hand side is then obtained using the same factorization.
Da Silva NV, Morgan J, MacGregor L, et al., 2009, An approach for multisource 3-D marine CSEM modelling in the frequency-domain, Pages: 883-887
Geophysical multi-source electromagnetic modelling is usually performed solving a linear system of equations for each right-hand side. This approach can be prohibitively expensive when the system of equations has a large number of degrees of fredom and sources. We present an alternative method for multi-source forward modelling of marine CSEM data. For the discretization of the electric field equation we use edge finite elements which naturally satisfy the material interface conditions for the electric field and avoid the presence of spurious modes in the solution. For solving the system of equations we use the software package MUMPS to factorize the system of equations. A solution for each right-hand side is then obtained using the same factorization.
Christeson GL, Collins GS, Morgan JV, et al., 2009, Mantle deformation beneath the Chicxulub impact crater, Earth and Planetary Science Letters, Vol: 284, Pages: 249-257, ISSN: 0012-821X
Collins GS, Morgan J, Barton P, et al., 2008, Dynamic modeling suggests terrace zone asymmetry in the Chicxulub crater is caused by target heterogeneity, EARTH PLANET SC LETT, Vol: 270, Pages: 221-230, ISSN: 0012-821X
Gulick SPS, Barton PJ, Christeson GL, et al., 2008, Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater, Nature Geoscience, Vol: 1
Warner M, Stekl I, Umpleby A, 2008, 3D wavefield tomography: Synthetic and field data examples, SEG Technical Program Expanded Abstracts, Vol: 27, Pages: 3330-3334, ISSN: 1052-3812
Full wavefield tomography has become well established in two dimensions, but its extension into 3D for realistically sized problems is computationally daunting. In this paper, we present one of the first studies to apply 3D wavefield tomography to field data, and demonstrate that the method can solve useful exploration problems that that are not tractable by other methods.
Warner M, Stekl I, Umpleby A, 2008, Efficientand effective 3D wavefield tomography, 70th European Association of Geoscientists and Engineers Conference and Exhibition 2008: Leveraging Technology. Incorporating SPE EUROPEC 2008, Vol: 3, Pages: 1607-1611
We demonstrate 3D wavefield tomography applied to surface-streamer seismic data and obtain a result which appears to remove the distoring effects of shallow high-velocity channels.
Warner M, Stekl I, Umpleby A, 2007, Full wavefield seismic tomography - Iterative forward modelling, in 3D, 69th European Association of Geoscientists and Engineers Conference and Exhibition 2007: Securing The Future. Incorporating SPE EUROPEC 2007, Vol: 2, Pages: 888-892
We have developed an efficient iterative solver for the 3D, two-way, acoustic wave equation, and demonstrate its use for 3D wavefield tomography on a synthetic seismic model. Using composite shots for the tomography, the method is sufficiently fast that it can be used to image realistic-sized field datasets.
Stekl I, Warner MR, Umpleby AP, 2007, 3D frequency domain waveform inversion - Synthetic shallow channel example, 69th European Association of Geoscientists and Engineers Conference and Exhibition 2007: Securing The Future. Incorporating SPE EUROPEC 2007, Vol: 2, Pages: 893-897
We are presenting a first example of 3D frequency domain acoustic inversion applied to a synthetics data over a shallow channel. High resolution images are obtained in less than a day CPU time using inexpensive hardware by utilizing a point iterative solver for wave equation modelling part of the code and multi shot approach. Tests have shown that it is possible to combine multiple shot positions and reduce time required for computation dramatically. Final recovered velocities are within 4% of the true velocity once and spatial positioning I quite well. We did not use any apriori information on anomaly position nor size.
Chironi C, Morgan JV, Warner MR, 2006, Imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 111, ISSN: 2169-9313
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- Citations: 15
Tong CH, Lana C, White RS, et al., 2005, Subsurface tectonic structure between overlapping mid-ocean ridge segments, GEOLOGY, Vol: 33, Pages: 409-412, ISSN: 0091-7613
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- Citations: 6
Barton P, Owen T, Gulick S, et al., 2005, Seismics in the environmental spotlight: Counting the cost, Pages: 29-32
Early in 2005 the US research vessel R/V Maurice Ewing, operated by Lamont-Doherty Earth Observatory at Columbia University, conducted an academic seismic survey of the Chicxulub impact crater in the shallow water offshore Yucatan, Mexico. This survey was the focus of a campaign by environmental activists, which enhanced local concerns in Mexico. A combination of US legal requirements and Mexican government restrictions resulted in highly restricted time windows in which the work could be conducted. Although the survey was ultimately successful, the costs escalated significantly, and the data return was less than originally planned. Here we analyse the nature of these costs, consider the extent to which these additional precautions helped to protect the environment, and examine strategies for minimizing unnecessary expenditure, preventing misinformation and ensuring environmental protection for future surveys.
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