Publications
113 results found
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.
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.
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.
Artemieva N, Morgan J, 2009, Modeling the formation of the K-P boundary layer, Icarus, Vol: 201, Pages: 768-780, ISSN: 0019-1035
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
Grieve RAF, Reimold U, Morgan JV, et al., 2008, Observations and interpretations at Vredefort, Sudbury and Chicxulub: Towards a composite model of a terrestrial impact basin, Meteoritics and Planetary Science, Vol: 43, Pages: 855-882
Morgan JV, 2008, Comment on "Determining Chondritic Impactor Size from the Marine Osmium Isotope Record", Science, Vol: 321, Pages: 1158-1158
Paquay et al. (Reports, 11 April 2008, p. 214) report that Osmium isotope ratios in marine sediments can be used to determine the size of a chondritic impacting body. Their assumptions, however, on the fate of an impacting projectile are incorrect, as only a small, unpredictable fraction of the impactor ends up dissolved in seawater.
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
Morgan J, Christeson G, Gulick S, et al., 2007, Joint IODP/ICDP scientific drilling of the Chicxulub impact crater, Scientific Drilling, Vol: 4, Pages: 42-44, ISSN: 1816-8957
Morgan J V, Lana C, Kearsley A, et al., 2006, Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub, Earth and Planetary Science Letters, Vol: 251, Pages: 264-279, ISSN: 0012-821X
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.
Morgan J, Warner M, Urrutia-Fucugauchi J, et al., 2005, Chicxulub crater seismic survey prepares way for future drilling, EOS, Transactions, American Geophysical Union, Vol: 86, Pages: 325-328, ISSN: 0096-3941
Wunnemann K, Morgan J, Jodicke H, 2005, Is Ries crater typical for its size? An analysis based upon old and new geophysical data and numerical modeling, Large Meteorite Impacts III, Editors: Kenkmann T, Horz F, Deutsch A, Boulder, Co, USA, Publisher: The Geological Society of America, Pages: 67-84, ISBN: 9780813723846
Morgan RPL, Barton PJ, Warner M, et al., 2000, Lithospheric structure north of Scotland -: I.: <i>P</i>-wave modelling, deep reflection profiles and gravity, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 142, Pages: 716-736, ISSN: 0956-540X
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- Citations: 20
Snyder DB, Hobbs RW, Britan J, et al., 1999, Ringed structural zones with deep roots formed by the Chicxulub impact, Journal of Geophysical Research: Solid Earth, Vol: 104, Pages: 10743-10755, ISSN: 2169-9313
The Chicxulub meteorite/comet impact of 65 Ma occurred on the present northeast coast of the Yucatan peninsula of Mexico and is considered by many to have caused a mass extinction at the end of the Cretaceous period. Impact craters are traditionally described in terms of ring structures. Deeply rooted faults underlying four previously recognized ring zones of the Chicxulub impact crater, as revealed on new deep seismic reflection profiles, demonstrate the catastrophic and diverse deformations that produced these zones. The innermost annular zone at Chicxulub coincides with a central peak ring. The seismic data show that the peak ring is composed of low-velocity (<5 km s-1), chaotically reflective material, interpreted as impact breccia, lying on top of blocks of pre-impact strata that were downdropped 4-6 km. Normal faults within the Cretaceous strata and deep, inward dipping reflections characterize two deformation zones at radial distances of 55-65 and 85-98 km. These normal faults accommodated the collapse, during the modification stage of crater development, of large (radial width of 5-25 km) blocks of pre-impact strata uplifted during the excavation stage. The structures root in the lower crust at depths of 15-30 km. Blind thrusts indicated by monoclines in pre-impact sedimentary rocks and deep, inward dipping reflections within the crystalline basement mark the outermost ring of deformation. These monoclines correlate with small topographic changes on the Cretaceous-Tertiary boundary layer at radial distances of 120-135 km. Palinspastic restoration of coherent blocks of downdropped pre-impact strata enabled improved estimates of the size and shape of the hole formed by the impact in a prominent reflector at 3- to 4-km depth. This hole is slightly elliptical along a SE-NW major axis (radius of 68 versus 63 km). Copyright 1999 by the American Geophysical Union.
Morgan JV, Warner M, 1999, Morphology of the Chicxulub impact: Peak-ring crater or multi-ring basin?, Large Meteorite Impacts and Planetary Evolution Ii, Pages: 281-290
Maguire PKH, Mackenzie GD, Denton P, et al., 1998, Preliminary results from a passive seismic array over the Chicxulub impact structure in Mexico, Geological Society Special Publication, Vol: 140, Pages: 177-193, ISSN: 0305-8719
This paper is part of the special publication Meteorites: flux with time and impact effects (eds M.M. Grady, R. Hutchinson, G.J.H. McCall and D.A. Rothery). A passive, 20-element, short-period (1 Hz) and broadband seismic array was deployed over the Chicxulub impact structure for c.100 days in early 1996. The principal objective was to study the shear-wave anisotropy associated with the structure; in particular, to determine the presence (or absence) of radial symmetry which will allow comment on the time variance of that anisotropy. A total of 15 teleseismic, 75 regional, and 100 local events were recorded. Preliminary results from studies of the surface-wave dispersion of the local events, and a receiver function analysis of a single teleseismic event are reported here. Thirty local events have been located, a number of which originated from quarries within the array. Analysis of seismograms from three of these events demonstrates a bimodal distribution; those whose ray-paths cross the outer part of the impact structure show a strong inverse dispersion, whereas those with ray-paths crossing the centre do not. The pattern may be produced by the sedimentary depositional environment, with deeper water sedimentation in the outer part of the post- impact crater basin and shallower water sedimentation over the upraised peak-ring block at the centre. Receiver functions derived for an event originating in Peru are dominated by an efficient mode conversion, simply modelled as a P-S multiple from the base Tertiary boundary. This shows a strong correlation with distance from the centre of the impact structure and implies it has an S-wave radial symmetry. The multiple also has a variable delay probably related to the depth of the conversion boundary. Unfortunately, the Moho conversion occurs at almost exactly the same time as this surface layer sediment multiple, restricting any modelling of Moho topography and its influence on the receiver functions.
Morgan JV, Warner MR, Chicxulub Working Group, 1997, Size and morphology of the Chicxulub impact crater, Nature, Vol: 390, Pages: 472-476
Warner MR, Morgan JV, Barton P, et al., 1996, Seismic reflections from the mantle represent relict subduction zones within the continental lithosphere, Geology, Vol: 24, Pages: 39-42
MORGAN JV, BARTON PJ, 1990, A GEOPHYSICAL-STUDY OF THE HATTON BANK VOLCANIC MARGIN - A SUMMARY OF THE RESULTS FROM A COMBINED SEISMIC, GRAVITY AND MAGNETIC EXPERIMENT, TECTONOPHYSICS, Vol: 173, Pages: 517-526, ISSN: 0040-1951
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- Citations: 22
MORGAN JV, BARTON PJ, WHITE RS, 1989, THE HATTON BANK CONTINENTAL-MARGIN .3. STRUCTURE FROM WIDE-ANGLE OBS AND MULTICHANNEL SEISMIC REFRACTION PROFILES, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 98, Pages: 367-384, ISSN: 0956-540X
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- Citations: 76
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