40 results found
Agudo ÒC, Da Silva NV, Warner M, et al., 2018, Acoustic full-waveform inversion in an elastic world, Geophysics, Vol: 83, Pages: R257-R271, ISSN: 0016-8033
© The Authors. Full-waveform inversion (FWI) is a technique used to obtain high-quality velocity models of the subsurface. Despite the elastic nature of the earth, the anisotropic acoustic wave equation is typically used to model wave propagation in FWI. In part, this simplification is essential for being efficient when inverting large 3D data sets, but it has the adverse effect of reducing the accuracy and resolution of the recovered P-wave velocity models, as well as a loss in potential to constrain other physical properties, such as the S-wave velocity given that amplitude information in the observed data set is not fully used. Here, we first apply conventional acoustic FWI to acoustic and elastic data generated using the same velocity model to investigate the effect of neglecting the elastic component in field data and we find that it leads to a loss in resolution and accuracy in the recovered velocity model. Then, we develop a method to mitigate elastic effects in acoustic FWI using matching filters that transform elastic data into acoustic data and find that it is applicable to marine and land data sets. Tests show that our approach is successful: The imprint of elastic effects on the recovered P-wave models is mitigated, leading to better-resolved models than those obtained after conventional acoustic FWI. Our method requires a guess of V P /V S and is marginally more computationally demanding than acoustic FWI, but much less so than elastic FWI.
Christeson GL, Gulick SPS, Morgan JV, et al., 2018, Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364, Earth and Planetary Science Letters, Vol: 495, Pages: 1-11, ISSN: 0012-821X
© 2018 Elsevier B.V. Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900–3700 m/s, 2.06–2.37 g/cm 3 , and 20–35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements of 3650–4350 m/s, density measurements of 2.26–2.37 g/cm 3 , and porosity measurements of 19–22%. We associate the low velocity, low density, and high porosity of suevite and impact melt rock with rapid emplacement, hydrothermal alteration products, and observations of pore space, vugs, and vesicles. The uplifted granitic peak ring materials have values of 4000–4200 m/s, 2.39–2.44 g/cm 3 , and 8–13% for velocity, density, and porosity, respectively; these values differ significantly from typical unaltered granite which has higher velocity and density, and lower porosity. The majority of Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable rock damage, and are consistent with numerical model predictions for peak-ring formation where the lithologies present within the peak ring represent some of the most shocked and damaged rocks in an impact basin. We integrate our results with previous seismic datasets to map the suevite near the borehole. We map suevite below the Paleogene sedimentary rock in the annular trough, on the peak ring, and in the central basin, implying that, post impact, suevite covered the entire floor of the impact basin. Suevite thickness is 100&nd
Davy RG, Morgan JV, Minshull TA, et al., 2018, Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 212, Pages: 244-263, ISSN: 0956-540X
Arnoux GM, Toomey DR, Hooft EEE, et al., 2017, Seismic evidence that black smoker heat flux is influenced by localized magma replenishment and associated increases in crustal permeability, Geophysical Research Letters, Vol: 44, Pages: 1687-1695, ISSN: 0094-8276
©2017. American Geophysical Union. All Rights Reserved. Hydrothermal circulation at mid-ocean ridges is responsible for ~25% of Earth's heat flux and controls the thermal and chemical evolution of young oceanic crust. The heat flux of black smoker hydrothermal systems is thought to be primarily controlled by localized magma supply and crustal permeability. Nevertheless, magma chamber characteristics and the nature of crustal permeability beneath such systems remain unclear. Here we apply three-dimensional full-waveform inversion to seismic data from the hydrothermally active Endeavour segment of the Juan de Fuca Ridge to image the upper crust in high resolution. We resolve velocity variations directly above the axial magma chamber that correlate with variations in seismicity, black smoker heat flux, and the depth of the axial magmatic system. We conclude that localized magma recharge to the axial magma lens, along with induced seismogenic cracking and increased permeability, influences black smoker heat flux.
Artemieva N, Morgan J, 2017, Quantifying the Release of Climate-Active Gases by Large Meteorite Impacts With a Case Study of Chicxulub, Geophysical Research Letters, ISSN: 0094-8276
Kring DA, Claeys P, Gulick SPS, et al., 2017, Chicxulub and the exploration of large peak-ring impact craters through scientific drilling, GSA Today, Vol: 27, Pages: 4-8, ISSN: 1052-5173
Copyright 2017, The Geological Society of America. The Chicxulub crater is the only wellpreserved peak-ring crater on Earth and linked, famously, to the K-T or K-Pg mass extinction event. For the first time, geologists have drilled into the peak ring of that crater in the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364. The Chicxulub impact event, the environmental calamity it produced, and the paleobiological consequences are among the most captivating topics being discussed in the geologic community. Here we focus attention on the geological processes that shaped the ~200-km-wide impact crater responsible for that discussion and the expedition's first year results.
Morgan JV, Artemieva NA, 2017, CLIMATIC GASES RELEASED FROM THE CHICXULUB IMPACT, 80th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: A244-A244, ISSN: 1086-9379
Rae ASP, Collins GS, Grieve RAF, et al., 2017, Complex crater formation: Insights from combining observations of shock pressure distribution with numerical models at the West Clearwater Lake impact structure, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 1330-1350, ISSN: 1086-9379
Morgan J, Warner M, Arnoux G, et al., 2016, Next-generation seismic experiments - II: wide-angle, multi-azimuth, 3-D, full-waveform inversion of sparse field data, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 204, Pages: 1342-1363, ISSN: 0956-540X
Morgan JV, Gulick SPS, Bralower T, et al., 2016, The formation of peak rings in large impact craters, SCIENCE, Vol: 354, Pages: 878-882, ISSN: 0036-8075
Silverton A, Warner M, Morgan J, et al., 2016, Offset-variable density improves acoustic full-waveform inversion: a shallow marine case study, GEOPHYSICAL PROSPECTING, Vol: 64, Pages: 1201-1214, ISSN: 0016-8025
Belcher CM, Hadden RM, Rein G, et al., 2015, An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous-Palaeogene impact at Chicxulub, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 172, Pages: 175-185, ISSN: 0016-7649
Bray VJ, Collins GS, Morgan JV, et al., 2014, Hydrocode simulation of Ganymede and Europa cratering trends - How thick is Europa's crust?, ICARUS, Vol: 231, Pages: 394-406, ISSN: 0019-1035
Gulick SPS, Christeson GL, Barton PJ, et al., 2013, GEOPHYSICAL CHARACTERIZATION OF THE CHICXULUB IMPACT CRATER, REVIEWS OF GEOPHYSICS, Vol: 51, Pages: 31-52, ISSN: 8755-1209
Morgan J, Artemieva N, Goldin T, 2013, Revisiting wildfires at the K-Pg boundary, Journal of Geophysical Research: Biogeosciences, Vol: 118, Pages: 1508-1520, ISSN: 2169-8953
Morgan J, Rebolledo-Vieyra M, 2013, Geophysical studies of impact craters, Impact Cratering, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, Pages: 211-222, ISBN: 9781405198295
Morgan J, Warner M, Bell R, et al., 2013, Next-generation seismic experiments: wide-angle, multi-azimuth, three-dimensional, full-waveform inversion, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 195, Pages: 1657-1678, ISSN: 0956-540X
Christeson GL, Morgan JV, Warner MR, 2012, Shallow oceanic crust: Full waveform tomographic images of the seismic layer 2A/2B boundary, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 117, ISSN: 2169-9313
Vieira da Silva N, Morgan JV, MacGregor L, et al., 2012, A finite element multifrontal method for 3D CSEM modeling in the frequency domain, Geophysics, Vol: 77, Pages: E101-E115
There has been a recent increase in the use of controlled-source electromagnetic (CSEM) surveys in the exploration for oil and gas. We developed a modeling scheme for 3D CSEM modeling in the frequency domain. The electric field was decomposed in primary and secondary components to eliminate the singularity originated by the source term. The primary field was calculated using a closed form solution, and the secondary field was computed discretizing a second-order partial differential equation for the electric field with the edge finite element. The solution to the linear system of equations was obtained using a massive parallel multifrontal solver, because such solvers are robust for indefinite and ill-conditioned linear systems. Recent trends in parallel computing were investigated for their use in mitigating the computational overburden associated with the use of a direct solver, and of its feasibility for 3D CSEM forward modeling with the edge finite element. The computation of the primary field was parallelized, over the computational domain and the number of sources, using a hybrid model of parallelism. When using a direct solver, the attainment of multisource solutions was only competitive if the same factors are used to achieve a solution for multi right-hand sides. This aspect was also investigated using the presented methodology. We tested our proposed approach using 1D and 3D synthetic models, and they demonstrated that it is robust and suitable for 3D CSEM modeling using a distributed memory system. The codes could thus be used to help design new surveys, as well to estimate subsurface conductivities through the implementation of an appropriate inversion scheme.
da Silva NV, Morgan JV, MacGregor L, et al., 2012, A finite element multifrontal method for 3D CSEM modeling in the frequency domain, GEOPHYSICS, Vol: 77, Pages: E101-E115, ISSN: 0016-8033
Kamo SL, Lana C, Morgan JV, 2011, U-Pb ages of shocked zircon grains link distal K-Pg boundary sites in Spain and Italy with the Chicxulub impact, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 310, Pages: 401-408, ISSN: 0012-821X
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-SOLID EARTH, Vol: 116, ISSN: 2169-9313
Barton PJ, Grieve RAF, Morgan JV, et al., 2010, Seismic images of Chicxulub impact melt sheet and comparison with the Sudbury structure, Pages: 103-113
Chicxulub is the only known impact structure on Earth with a fully preserved peak ring, and it forms an important natural laboratory for the study of large impact structures and understanding of large-scale cratering on Earth and other planets. Seismic data collected in 1996 and 2005 reveal detailed images of the uppermost crater in the central basin at Chicxulub. Seismic reflection profiles show a reflective layer ∼1 km beneath the apparent crater floor, topped by upwardly concave reflectors interpreted as saucer-shaped sills. The upper part of this reflective layer is coincident with a thin high-velocity layer identified by analyzing refractions on the 6 km seismic streamer data. The high-velocity layer is almost horizontal and appears to be contained within the peak ring structure. We argue that this reflective layer is the predicted coherent melt sheet formed during impact, and it may be comparable with the unit known as the Sudbury Igneous Complex at the Sudbury impact structure. The Sudbury Igneous Complex, interpreted as a differentiated impact melt sheet, appears to have a similar scale and geometry, and an uppermost lithological sequence consisting of a high velocity layer at the top and a velocity inversion beneath. This comparison suggests that the Chicxulub impact structure also contains a coherent differentiated melt sheet. © 2010 The Geological Society of America. All rights reserved.
Grieve RAF, Ames DE, Morgan JV, et al., 2010, The evolution of the Onaping Formation at the Sudbury impact structure, METEORITICS & PLANETARY SCIENCE, Vol: 45, Pages: 759-782, ISSN: 1086-9379
Schulte P, Alegret L, Arenillas I, et al., 2010, The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary, SCIENCE, Vol: 327, Pages: 1214-1218, ISSN: 0036-8075
Artemieva N, Morgan J, 2009, Modeling the formation of the K-Pg boundary layer, ICARUS, Vol: 201, Pages: 768-780, ISSN: 0019-1035
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 AND PLANETARY SCIENCE LETTERS, Vol: 270, Pages: 221-230, ISSN: 0012-821X
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