Imperial College London

ProfessorJoannaMorgan

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Geophysics
 
 
 
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Contact

 

+44 (0)20 7594 6423j.v.morgan

 
 
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Location

 

2.38BRoyal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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76 results found

Rasmussen C, Stockli DF, Ross CH, Pickersgill A, Gulick SP, Schmieder M, Christeson GL, Wittmann A, Kring DA, Morgan JVet al., 2019, U-Pb memory behavior in Chicxulub's peak ring — Applying U-Pb depth profiling to shocked zircon, Chemical Geology, Vol: 525, Pages: 356-367, ISSN: 0009-2541

© 2019 Elsevier B.V. The zircon U-Pb system is one of the most robust geochronometers, but during an impact event individual crystals can be affected differently by the passage of the shock wave and impact generated heat. Unraveling the potentially complex thermal history recorded by zircon crystals that experienced variable levels of shock and heating, as well as additioanl pre- and post-impact thermal events, has been difficult using classical geochronological methods. The existing high-precision 40Ar/39Ar age constraints for the K-Pg Chicxulub event, and the previous U-Pb dating of the basement rocks from the impact site, make Chicxulub an ideal location to study impact-induced effects on the zircon U-Pb systematics and to evaluate potential 'memory effects' of pre-impact U-Pb signatures preserved within those individual zircon crystals. Recent IODP-ICDP drilling of the Chicxulub impact structure recovered 580 m of uplifted shocked granitoid and 130 m of melt and suevite, providing an unprecedented opportunity to study zircon crystals subjected to a range of shock pressures, thermal, and deformational histories. Zircon morphologies were classified using scanning electron microscopy (SEM) imaging and then samples were depth profiled using laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) to document the range of preserved age domains from rim-to-center within individual crystals. The results show U-Pb ages range from 66 to 472 Ma, which are consistent with both inherited Carboniferous and Late Paleozoic basement ages as well as Pb loss ages in response to the K-Pg impact event. While the bulk of the zircon grains preserve Paleozoic ages, high U (metamict) zones within fractured zircon crystals exhibited an age within uncertainty (66 ± 6.2 Ma) of the impact age (66.038 ± 0.049 Ma), indicating that inherited intragrain U-Pb kinetics and/or hydrothermal fluid flow may have controlled age resetting those zircon crystals rather

Journal article

Gulick SPS, Bralower T, Ormö J, Hall B, Grice K, Schaefer B, Lyons S, Freeman KH, Morgan J, Artemieva N, Kaskes P, de Graaff SJ, Whalen M, Collins G, Tikoo SM, Verhagen C, Christeson GL, Claeys P, Coolen M, Goderis S, Goto K, Grieve R, McCall N, Osinski G, Rae A, Riller U, Smit J, Vajda V, Wittmann A, and the Expedition 364 Scientistset al., 2019, The first day of the cenozoic, Proceedings of the National Academy of Sciences, ISSN: 0027-8424

Journal article

Gray M, Bell R, Morgan J, Henrys S, Barker D, IODP Expedition 372 scientists, IODP Expedition 375 scientistset al., 2019, Imaging the shallow subsurface structure of the north Hikurangi subduction zone, New Zealand, using 2D full-waveform inversion, Journal of Geophysical Research. Solid Earth, ISSN: 2169-9356

The northern Hikurangi plate boundary fault hosts a range of seismic behaviors, of which the physical mechanisms controlling seismicity are poorly understood, but often related to high pore fluid pressures and conditionally stable frictional conditions. Using 2D marine seismic streamer data, we employ full-waveform inversion (FWI) to obtain a high-resolution 2D P-wave velocity model across the Hikurangi margin down to depths of ~2 km. The validity of the FWI velocity model is investigated through comparison with the pre-stack depth migrated seismic reflection image, sonic well data, and the match between observed and synthetic waveforms. Our model reveals the shallow structure of the overriding plate, including the fault plumbing system above the zone of SSEs to theoretical resolution of a half seismic wavelength. We find that the hanging walls of thrust faults often have substantially higher velocities than footwalls, consistent with higher compaction. In some cases, intra-wedge faults identified from reflection data are associated with low-velocity anomalies, which may suggest they are high-porosity zones acting as conduits for fluid flow. The continuity of velocity structure away from IODP drill site U1520 suggests that lithological variations in the incoming sedimentary stratigraphy observed at this site continue to the deformation front and are likely important in controlling seismic behavior. This investigation provides a high-resolution insight into the shallow parts of subduction zones, which shows promise for the extension of modeling to 3D using a recently-acquired, longer-offset, seismic dataset.

Journal article

Rae ASP, Collins G, Morgan J, Salge T, Christeson GL, Leung J, Lofi J, Gulick SPS, Poelchau M, Riller U, Gebhardt C, Grieve RA, Osinski GRet al., Impact-induced porosity and micro-fracturing at the Chicxulub impact structure, Journal of Geophysical Research: Planets, ISSN: 2169-9097

Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave-speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small scale petrographic and petrophysical measurements with larger scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced micro-fracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak-ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak-ring formation, can accurately predict the distribution and orientation of impact-induced micro-fractures in large craters which plays an important role in the geophysical signature of impact structures.

Journal article

Hooft EEE, Heath BA, Toomey DR, Paulatto M, Papazachos CB, Nomikou P, Morgan JV, Warner MRet al., 2019, Seismic imaging of Santorini: Subsurface constraints on caldera collapse and present-day magma recharge, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 514, Pages: 48-61, ISSN: 0012-821X

Journal article

Timms NE, Pearce MA, Erickson TM, Cavosie AJ, Rae ASP, Wheeler J, Wittmann A, Ferriere L, Poelchau MH, Tomioka N, Collins GS, Gulick SPS, Rasmussen C, Morgan JV, Gulick SPS, Morgan JV, Chenot E, Christeson GL, Claeys P, Cockell CS, Coolen MJL, Ferriere L, Gebhardt C, Goto K, Green S, Jones H, Kring DA, Lofi J, Lowery CM, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau MH, Rae ASP, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo SM, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Wittmann A, Xiao L, Yamaguchi KEet al., 2019, New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico, Contributions to Mineralogy and Petrology, Vol: 174, ISSN: 0010-7999

Accessory mineral geochronometers such as apatite, baddeleyite, monazite, xenotime and zircon are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity-impact processes. To date, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and a U–Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoid from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired core from the International Ocean Discovery Program Hole M0077A preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1) = ~  {1¯11} , and shear direction (η1) = < 110 > , and less commonly with the mode K1 = {130}, η1 = ~ <522 > . In some grains, {130} deformation bands have formed concurrently with the deformation twins, indicating dislocation slip with Burgers vector b = < 341 > can be active during impact metamorphism. Titanite twins in the modes described here have not been reported from endogenically deformed rocks; we, therefore, propose this newly identified twin form as a result of shock deformation. Formation conditions of the twins have not been experimentally calibrated, and are here empirically constrained by the presence of planar deformation features in quartz (12 ± 5 and ~ 17 ± 5 GPa) and the absence of shock twins in zircon (< 20 GPa). While the lower threshold of titanite twin formation remains poorly constrained, identification of these twins highlight the utility of titanite as a shock indicator over the pressure range between 12 and 17 GPa. Given the challenges to find diagnostic indicators of shock metamorphism to identify both ancient

Journal article

Urrutia-Fucugauchi J, Pérez-Cruz L, Morgan J, Gulick S, Wittmann A, Lofi J, Morgan JV, Gulick SPS, Chenot E, Christeson G, Claeys P, Cockell C, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Jones H, Kring DA, Lofi J, Lowery C, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill A, Poelchau M, Rae A, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo-Schantz S, Tomioka N, Urrutia-Fucugauchi J, Whalen M, Wittmann A, Xiao L, Yamaguchi KE, Bralower T, Collins GSet al., 2019, Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism, Geology Today, Vol: 35, Pages: 68-72, ISSN: 0266-6979

© 2019 John Wiley & Sons Ltd, The Geologists' Association & The Geological Society of London The IODP-ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well-preserved peak ring. The borehole penetrated a sequence of post-impact carbonates and a unit of suevites and clast-poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre-impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long-distance transport of weakened material during collapse of the transient cavity and final crater formation.

Journal article

Lowery CM, Morgan J, Gulick SPS, Bralower TJ, Christeson GL, Chenot E, Claeys P, Cockell C, Coolen MJL, Ferriere L, Gebhardt C, Goto K, Green S, Jones H, Kring DA, Lofi J, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill A, Poelchau M, Rae A, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo S, Tomioka N, Urrutia-Fucugauchi J, Whalen M, Wittmann A, Xiao L, Yamaguchi Ket al., 2019, OCEAN DRILLING PERSPECTIVES ON Meteorite Impacts, OCEANOGRAPHY, Vol: 32, Pages: 120-134, ISSN: 1042-8275

Journal article

Rae A, Collins G, Poelchau M, Riller U, Davison T, Grieve R, Osinski G, Morgan J, IODPICDP Expedition 364 Scientistset al., 2019, Stress-strain evolution during peak-ring formation: a case study of the Chicxulub impact structure, Journal of Geophysical Research: Planets, ISSN: 2169-9097

Deformation is a ubiquitous process that occurs to rocks during impact cratering; thus, quantifying the deformation of those rocks can provide first‐order constraints on the process of impact cratering. Until now, specific quantification of the conditions of stress and strain within models of impact cratering has not been compared to structural observations. This paper describes a methodology to analyze stress and strain within numerical impact models. This method is then used to predict deformation and its cause during peak‐ring formation: a complex process that is not fully understood, requiring remarkable transient weakening and causing a significant redistribution of crustal rocks. The presented results are timely due to the recent Joint International Ocean Discovery Program and International Continental Scientific Drilling Program drilling of the peak ring within the Chicxulub crater, permitting direct comparison between the deformation history within numerical models and the structural history of rocks from a peak ring. The modeled results are remarkably consistent with observed deformation within the Chicxulub peak ring, constraining the following: (1) the orientation of rocks relative to their preimpact orientation; (2) total strain, strain rates, and the type of shear during each stage of cratering; and (3) the orientation and magnitude of principal stresses during each stage of cratering. The methodology and analysis used to generate these predictions is general and, therefore, allows numerical impact models to be constrained by structural observations of impact craters and for those models to produce quantitative predictions.

Journal article

Riller U, Poelchau MH, Rae ASP, Schulte FM, Collins GS, Melosh HJ, Grieve RAF, Morgan JV, Gulick SPS, Lofi J, Diaw A, McCall N, Kring DA, IODPIC DP Expedition 364 Science Partyet al., 2018, Author Correction: Rock fluidization during peak-ring formation of large impact structures., Nature, Vol: 564, Pages: E36-E36

In this Article, the middle initial of author Kosei E. Yamaguchi (of the IODP-ICDP Expedition 364 Science Party) was missing and his affiliation is to Toho University (not Tohu University). These errors have been corrected online.

Journal article

Bentham H, Morgan JV, Angus D, 2018, Investigating the use of 3D full-waveform inversion to characterise the host rock at a geological disposal site, Geophysical Journal International, Vol: 215, Pages: 2035-2046, ISSN: 0956-540X

The U.K. government has a policy to dispose of higher activity radioactive waste in a geological disposal facility (GDF), which will have multiple protective barriers to keep the waste isolated and to ensure no harmful quantities of radioactivity are able to reach the surface. Currently no specific GDF site in the United Kingdom has been chosen but, once it has, the site is likely to be investigated using seismic methods. In this study, we explore whether 3-D full-waveform inversion (FWI) of seismic data can be used to map changes in physical properties caused by the construction of the site, specifically tunnel-induced fracturing. We have built a synthetic model for a GDF located in granite at 1000 m depth below the surface, since granite is one of the candidate host rocks due to its high strength and low permeability and the GDF could be located at such a depth. We use an effective medium model to predict changes in P-wave velocity associated with tunnel-induced fracturing, within the spatial limits of an excavated disturbed zone (EdZ), modelled here as an increase in fracture density around the tunnel. We then generate synthetic seismic data using a number of different experimental geometries to investigate how they affect the performance of FWI in recovering subsurface P-wave velocity structure. We find that the location and velocity of the EdZ are recovered well, especially when data recorded on tunnel receivers are included in the inversion. Our findings show that 3-D FWI could be a useful tool for characterizing the subsurface and changes in fracture properties caused during construction, and make a suite of suggestions on how to proceed once a potential GDF site has been identified and the geological setting is known.

Journal article

Agudo ÓC, Vieira Da Silva N, Warner M, Kalinicheva T, Morgan Jet al., 2018, Addressing viscous effects in acoustic full-waveform inversion, Geophysics, Vol: 83, Pages: R611-R628, ISSN: 0016-8033

In conventional full-waveform inversion (FWI), viscous effects are typically neglected, and this is likely to adversely affect the recovery of P-wave velocity. We have developed a strategy to mitigate viscous effects based on the use of matching filters with the aim of improving the performance of acoustic FWI. The approach requires an approximate estimate of the intrinsic attenuation model, and it is one to three times more expensive than conventional acoustic FWI. First, we perform 2D synthetic tests to study the impact of viscoacoustic effects on the recorded wavefield and analyze how that affects the recovered velocity models after acoustic FWI. Then, we apply the current method on the generated data and determine that it mitigates viscous effects successfully even in the presence of noise. We find that having an approximate estimate for intrinsic attenuation, even when these effects are strong, leads to improvements in resolution and a more accurate recovery of the P-wave velocity. Then, we implement and develop our method on a 2D field data set using Gabor transforms to obtain an approximate intrinsic attenuation model and inversion frequencies of up to 24 Hz. The analysis of the results indicates that there is an improvement in terms of resolution and continuity of the layers on the recovered P-wave velocity model, leading to an improved flattening of gathers and a closer match of the inverted velocity model with the migrated seismic data.

Journal article

Riller U, Poelchau MH, Rae A, Schulte FM, Collins GS, Melosh HJ, Grieve RAF, Morgan JV, Gulick SPS, Lofi J, Diaw A, McCall N, Kring DAet al., 2018, Rock fluidization during peak-ring formation of large impact structures, Nature, Vol: 562, Pages: 511-518, ISSN: 0028-0836

Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. Recent drilling of the approximately 200-km-diameter Chicxulub impact structure in Mexico has produced a record of brittle and viscous deformation within its peak-ring rocks. Here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting.

Journal article

Lofi J, Smith D, Delahunty C, Le Ber E, Brun L, Henry G, Paris J, Tikoo S, Zylberman W, Pezard PA, Célérier B, Schmitt DR, Nixon C, Gulick SPS, Morgan JV, Chenot E, Christeson GL, Claeys P, Cockell CS, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Green S, Jones H, Kring DA, Lowery CM, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau M, Rae ASP, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Wittmann A, Xiao L, Yamaguchi KE, Bralower TJet al., 2018, Drilling-induced and logging-related features illustrated from IODP-ICDP Expedition 364 downhole logs and borehole imaging tools, Scientific Drilling, Vol: 24, Pages: 1-13, ISSN: 1816-8957

Expedition 364 was a joint IODP and ICDP mission-specific platform (MSP) expedition to explore the Chicxulub impact crater buried below the surface of the Yucatán continental shelf seafloor. In April and May 2016, this expedition drilled a single borehole at Site M0077 into the crater's peak ring. Excellent quality cores were recovered from ~ 505 to ~1335m below seafloor (m b.s.f.), and high-resolution open hole logs were acquired between the surface and total drill depth. Downhole logs are used to image the borehole wall, measure the physical properties of rocks that surround the borehole, and assess borehole quality during drilling and coring operations. When making geological interpretations of downhole logs, it is essential to be able to distinguish between features that are geological and those that are operation-related. During Expedition 364 some drilling-induced and logging-related features were observed and include the following: effects caused by the presence of casing and metal debris in the hole, logging-tool eccentering, drilling-induced corkscrew shape of the hole, possible re-magnetization of low-coercivity grains within sedimentary rocks, markings on the borehole wall, and drilling-induced changes in the borehole diameter and trajectory.

Journal article

Christeson GL, Gulick SPS, Morgan JV, Gebhardt C, Kring DA, Le Ber E, Lofi J, Nixon C, Poelchau M, Rae ASP, Rebolledo-Vieyra M, Riller U, Schmitt DR, Wittmann A, Bralower TJ, Chenot E, Claeys P, Cockell CS, Coolen MJL, Ferrière L, Green S, Goto K, Jones H, Lowery CM, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Rasmussen C, Sato H, Smit J, Tikoo SM, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Xiao L, Yamaguchi KEet 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

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/cm3, 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/cm3, 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/cm3, 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 100–165 m on the top of the peak

Journal article

Magee C, Stevenson C, Ebmeier S, Keir D, Hammond J, Gottsmann J, Whaler K, Schofield N, Jackson C, Petronis M, O'Driscoll B, Morgan J, Cruden A, Vollgger S, Dering G, Micklethwaite S, Jackson Met al., 2018, Magma plumbing systems: a geophysical perspective, Journal of Petrology, Vol: 59, Pages: 1217-1251, ISSN: 0022-3530

Over the last few decades, significant advances in using geophysical techniques to image the structure of magma plumbing systems have enabled the identification of zones of melt accumulation, crystal mush development, and magma migration. Combining advanced geophysical observations with petrological and geochemical data has arguably revolutionised our understanding of, and afforded exciting new insights into, the development of entire magma plumbing systems. However, divisions between the scales and physical settings over which these geophysical, petrological, and geochemical methods are applied still remain. To characterise some of these differences and promote the benefits of further integration between these methodologies, we provide a review of geophysical techniques and discuss how they can be utilised to provide a structural context for and place physical limits on the chemical evolution of magma plumbing systems. For example, we examine how Interferometric Synthetic Aperture Radar (InSAR), coupled with Global Positioning System (GPS) and Global Navigation Satellite System (GNSS) data, and seismicity may be used to track magma migration in near real-time. We also discuss how seismic imaging, gravimetry and electromagnetic data can identify contemporary melt zones, magma reservoirs and/or crystal mushes. These techniques complement seismic reflection data and rock magnetic analyses that delimit the structure and emplacement of ancient magma plumbing systems. For each of these techniques, with the addition of full-waveform inversion (FWI), the use of Unmanned Aerial Vehicles (UAVs) and the integration of geophysics with numerical modelling, we discuss potential future directions. We show that approaching problems concerning magma plumbing systems from an integrated petrological, geochemical, and geophysical perspective will undoubtedly yield important scientific advances, providing exciting future opportunities for the volcanological community.

Journal article

Lowery CM, Bralower TJ, Owens JD, Rodríguez-Tovar FJ, Jones H, Smit J, Whalen MT, Claeys P, Farley K, Gulick SPS, Morgan JV, Green S, Chenot E, Christeson GL, Cockell CS, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Kring DA, Lofi J, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau MH, Rae ASP, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Tikoo SM, Tomioka N, Urrutia-Fucugauchi J, Vellekoop J, Wittmann A, Xiao L, Yamaguchi KE, Zylberman Wet al., 2018, Rapid recovery of life at ground zero of the end-Cretaceous mass extinction, Nature, Vol: 558, Pages: 288-291, ISSN: 0028-0836

The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth1,2. It was caused by the impact of an asteroid3,4 on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago 5 , forming the Chicxulub impact crater6,7. After the mass extinction, the recovery of the global marine ecosystem-measured as primary productivity-was geographically heterogeneous 8 ; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions8-11, taking 300 thousand years (kyr) to return to levels similar to those of the Late Cretaceous period. Delayed recovery of marine productivity closer to the crater implies an impact-related environmental control, such as toxic metal poisoning 12 , on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors-trophic interactions 13 , species incumbency and competitive exclusion by opportunists 14 -and 'chance'8,15,16. The question of whether the post-impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems. If there is a relationship between the distance from the impact and the recovery of marine productivity, we would expect recovery rates to be slowest in the crater itself. Here we present a record of foraminifera, calcareous nannoplankton, trace fossils and elemental abundance data from within the Chicxulub crater, dated to approximately the first 200 kyr of the Palaeocene. We show that life reappeared in the basin just years after the impact and a high-productivity ecosystem was established within 30 kyr, which indicates that proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery. Ecological processes probably controlled the recovery of productivity after the Cretaceous/Palae

Journal article

Calderon Agudo O, Vieira Da Silva N, Warner M, Morgan Jet al., 2018, Acoustic full-waveform inversion in an elastic world, Geophysics, Vol: 83, Pages: R257-R271, ISSN: 1942-2156

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 VP/VS and is marginally more computationally demanding than acoustic FWI, but much less so than elastic FWI.Read More: https://library.seg.org/doi/10.1190/geo2017-0063.1

Journal article

Morgan JV, Artemieva N, Expedition 364 Science Party, 2017, Quantifying the release of climate-active gases by large meteorite impacts with a case study of Chicxulub, Geophysical Research Letters, Vol: 44, Pages: 10180-10188, ISSN: 0094-8276

Potentially hazardous asteroids and comets have hit Earth throughout its history, with catastrophic consequences in the case of the Chicxulub impact. Here we reexamine one of the mechanisms that allow an impact to have a global effect—the release of climate-active gases from sedimentary rocks. We use the SOVA hydrocode and model ejected materials for a sufficient time after impact to quantify the volume of gases that reach high enough altitudes (> 25 km) to have global consequences. We vary impact angle, sediment thickness and porosity, water depth, and shock pressure for devolatilization and present the results in a dimensionless form so that the released gases can be estimated for any impact into a sedimentary target. Using new constraints on the Chicxulub impact angle and target composition, we estimate that 325 ± 130 Gt of sulfur and 425 ± 160 Gt CO2 were ejected and produced severe changes to the global climate.

Journal article

Davy RG, Morgan JV, Minshull TA, Bayrakci G, Bull JM, Klaeschen D, Reston TJ, Sawyer DS, Lymer G, Cresswell Det al., 2017, 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

Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.

Journal article

Kring DA, Claeys P, Gulick SPS, Morgan JV, Collins GSet 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

The Chicxulub crater is the only well-preserved 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.

Journal article

Arnoux G, Toomey D, Hooft E, Wilcock W, Morgan JV, Warner M, VanderBeek Bet 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: 1944-8007

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 remains 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.

Journal article

Rae A, Collins GS, Grieve RAF, Osinki GR, Morgan JVet 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

Large impact structures have complex morphologies, with zones of structural uplift that can be expressed topographically as central peaks and/or peak rings internal to the crater rim. The formation of these structures requires transient strength reduction in the target material and one of the proposed mechanisms to explain this behavior is acoustic fluidization. Here, samples of shock-metamorphosed quartz-bearing lithologies at the West Clearwater Lake impact structure, Canada, are used to estimate the maximum recorded shock pressures in three dimensions across the crater. These measurements demonstrate that the currently-observed distribution of shock metamorphism is strongly controlled by the formation of the structural uplift. The distribution of peak shock pressures, together with apparent crater morphology and geological observations, is compared with numerical impact simulations to constrain parameters used in the block-model implementation of acoustic fluidization. The numerical simulations produce craters that are consistent with morphological and geological observations. The results show that the regeneration of acoustic energy must be an important feature of acoustic fluidization in crater collapse, and should be included in future implementations. Based on the comparison between observational data and impact simulations we conclude that the West Clearwater Lake structure had an original rim (final crater) diameter of 35–40 km and has since experienced up to ~2 km of differential erosion.

Journal article

Agudo OC, Da Silva NV, Warner M, Morgan Jet al., 2017, Addressing viscous effects in acoustic full-waveform inversion

Seismic waves are attenuated and dispersed as they travel through the subsurface given that part of the energy is lost into heat. These effects are visible on the recorded seismic data but are commonly ignored when performing acoustic full-waveform inversion (FWI). As a result, the recovered P-wave velocity models are not as well resolved and are quantitatively less accurate. Here we analyse the impact of viscous effects in acoustic FWI of visco-acoustic synthetic data and we propose and apply a method to mitigate attenuation effects while still performing acoustic FWI, which is based on matching filters. We show that only a smooth model of attenuation is required to successfully improve the recovered P-wave velocity model, even when applied to a noisy synthetic dataset.

Conference paper

Morgan JV, 2016, The formation of peak rings in large impact craters, Science, Vol: 354, Pages: 878-882, ISSN: 0036-8075

Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.

Journal article

Morgan JV, Warner MR, Arnoux G, Hooft E, Toomey D, VanderBeek B, Wilcock Wet 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: 1365-246X

3-D full-waveform inversion (FWI) is an advanced seismic imaging technique that has been widely adopted by the oil and gas industry to obtain high-fidelity models of P-wave velocity that lead to improvements in migrated images of the reservoir. Most industrial applications of 3-D FWI model the acoustic wavefield, often account for the kinematic effect of anisotropy, and focus on matching the low-frequency component of the early arriving refractions that are most sensitive to P-wave velocity structure. Here, we have adopted the same approach in an application of 3-D acoustic, anisotropic FWI to an ocean-bottom-seismometer (OBS) field data set acquired across the Endeavour oceanic spreading centre in the northeastern Pacific. Starting models for P-wave velocity and anisotropy were obtained from traveltime tomography; during FWI, velocity is updated whereas anisotropy is kept fixed. We demonstrate that, for the Endeavour field data set, 3-D FWI is able to recover fine-scale velocity structure with a resolution that is 2–4 times better than conventional traveltime tomography. Quality assurance procedures have been employed to monitor each step of the workflow; these are time consuming but critical to the development of a successful inversion strategy. Finally, a suite of checkerboard tests has been performed which shows that the full potential resolution of FWI can be obtained if we acquire a 3-D survey with a slightly denser shot and receiver spacing than is usual for an academic experiment. We anticipate that this exciting development will encourage future seismic investigations of earth science targets that would benefit from the superior resolution offered by 3-D FWI.

Journal article

Agudo OC, da Silva NV, Warner M, Morgan Jet al., 2016, Acoustic full-waveform inversion in an elastic world, Pages: 1058-1062, ISSN: 1052-3812

© 2016 SEG. Despite the elastic nature of the earth, wave propagation in the subsurface is normally modeled using the acoustic anisotropic wave equation, in part due to the requirement to be efficient when dealing with large 3D datasets. This simplification has a negative effect on the quality of recovered P-wave models, as it means that amplitude information in the observed data cannot be fully utilized when applying full-waveform inversion (FWI) (Warner et al., 2013). We examine the consequences of using an acoustic wave propagator in two synthetic examples, and we propose a method to mitigate elastic effects in acoustic FWI based on matching filters. We find that our proposed approach is successful: the recovered P-wave models are better resolved than those obtained using conventional acoustic FWI.

Conference paper

Silverton A, Warner M, Morgan J, Umpleby Aet al., 2015, Offset-variable density improves acoustic full-waveform inversion: a shallow marine case study, Geophysical Prospecting, Vol: 64, Pages: 1201-1214, ISSN: 0016-8025

We have previously applied three-dimensional acoustic, anisotropic, full-waveform inversion to a shallow-water, wide-angle, ocean-bottom-cable dataset to obtain a high-resolution velocity model. This velocity model produced: an improved match between synthetic and field data, better flattening of common-image gathers, a closer fit to well logs, and an improvement in the pre-stack depth-migrated image. Nevertheless, close examination reveals that there is a systematic mismatch between the observed and predicted datafrom this full-waveform inversion model, with the predicted data being consistently delayed in time. We demonstrate that this mismatch cannot be produced by systematic errors in the starting model, by errors in the assumed source wavelet, by incomplete convergence, or by the use of an insufficiently fine finite-difference mesh. Throughout these tests, the mismatch is remarkably robustwith the significant exception that we do not see an analogous mismatch when inverting synthetic acoustic data. We suspect therefore that the mismatch arises because of inadequacies in the physics that are used during inversion. For ocean-bottom-cabledata in shallow water at low frequency, apparent observed arrival times, in wide-angle turning-ray data, result from the characteristics of the detailed interference pattern between primary refractions, surface ghosts, and a large suite of wide-angle multiple reflected and/or multiple refracted arrivals. In these circumstances, the dynamics of individual arrivals can strongly influence the apparent arrival times of the resultant compound waveforms. In acoustic full-waveform inversion, we do not normally know the density of the seabed, and we do not properly account for finite shear velocity, finite attenuation, and fine-scale anisotropy variation, all of which can influence the relative amplitudes of different interfering arrivals, which in their turn influence the apparent kinematics. Here, wedemonstrate that the introduction of

Journal article

Belcher CM, Hadden RM, Rein G, Morgan JV, Artemieva N, Goldin Tet 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

Journal article

Bray VJ, Collins GS, Morgan JV, Melosh HJ, Schenk PMet 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

Journal article

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