Download or read book Seismic Velocity Structure Associated with Gas Hydrate at the Frontal Ridge of Northern Cascadia Margin written by Caroll López and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: At the frontal ridge near the base of the slope off Vancouver Island, wide-angle ocean bottom seismometer (OBS) data were acquired in summer 2005, in support of the Integrated Ocean Drilling Program (IODP) Expedition 311. Marine gas hydrate is present beneath the ridge based on the observation of the 'Bottom Simulating Reflector' (BSR) that is interpreted to coincide with the base of the methane hydrate stability zone. Hydrate was also observed in downhole logs and drilling by IODP. The BSR has been identified on single-channel seismic data at -250-260 m depth beneath the ridge crest and on its seaward slope. The OBS data have been analyzed with the objective of determining the velocity structure in the upper portion of the accretionary wedge especially the hydrate stability zone and underlying free gas. As identified by a clear refracted phase, the velocity structure above the BSR shows anomalous high velocities of about 1.95 (?0.5) km/s at shallow depths of 80 - 110 m. On vertical incidence data, high amplitude reflectors are observed near this depth. Below the BSR, the velocities increase to -2.4 km/s at sub-seafloor depths of about 600 m. A strong refracted phase with a velocity of 4.0 km/s is generated at a depth of about 1700 mbsf. Velocities from traveltime inversion of OBS data are in general agreement with the Integrated Ocean Drilling Program (IODP) X311 downhole sonic velocities. In particular, on the log data, a layer with low porosity and high velocities of 2.4 - 2.8 km/s was observed at depths of 50 - 75 m. This probably corresponds with the 1.95 km/s layer at depths of 80-110 m interpreted from the OBS data. The refraction data thus suggest that this high-velocity layer varies laterally through the frontal ridge region, out to distances of at least 4 km from the drillhole. BSR depths (250-280 m) estimated in the present work also agree with the IODP X311 depths. From the velocity structure, we can make estimates of hydrate concentration in a region close to the deformation front, where fluid flow velocities are expected to be large. The gas hydrates concentrations vary from -35% for the shallow phase to -22% for the layer above the BSR. The deep refracted phase with a velocity of 4.0 km/s at 1700 m depth indicates the presence of highly compacted accreted wedge sediments. On the SW side of the frontal ridge, a collapse structure is observed in newly acquired multi-beam bathymetry data from the University of Washington and in seismic reflection data. The BSR is present in the region surrounding the slump. There are only weak indications of its presence within the slide region. Since hydrates may prevent normal sediment compaction, their dissociation in sediment pores is thought to decrease seafloor strength, potentially facilitating submarine landslides on continental slopes. The head wall of the frontal ridge slide is -250 m high, extending close to the BSR depth, and the slump has eroded a -2.5 km long section into the ridge, along strike. Migrated seismic reflection data image a set of normal faults in the frontal ridge striking NE-SW, perpendicular to the strike of the ridge and the direction of plate convergence. These faults outcrop at the seafloor and can be traced from the surface through the sedimentary section to depths well below the BSR in some locations. Seafloors scarps show that fault seafloor displacements of -25 m to 75 m are generated. The two faults with the largest seafloor scarps bound the region of slope failure on the frontal ridge, suggesting that the lateral extent of slumping is fault-controlled. The triggering mechanism for the slope failure may have been a combination of various effects. The possible mechanisms explored include gas hydrate dissociation, high pore pressure fluid expulsion along the faults, and salinity elevation in faults which would inhibit the formation of gas hydrates along the faults. However, an earthquake may induce initial slope failure, which can not only start gas hydrate dissociation but also increase fluid expulsion and pore pressure.
Download or read book Seismic Velocity Structure Associated with Gas Hydrate at the Frontal Ridge of Northern Cascadia Margin written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: At the frontal ridge near the base of the slope off Vancouver Island, wide-angle ocean bottom seismometer (OBS) data were acquired in summer 2005, in support of the Integrated Ocean Drilling Program (IODP) Expedition 311. Marine gas hydrate is present beneath the ridge based on the observation of the 'Bottom Simulating Reflector' (BSR) that is interpreted to coincide with the base of the methane hydrate stability zone. Hydrate was also observed in downhole logs and drilling by IODP. The BSR has been identified on single-channel seismic data at -250-260 m depth beneath the ridge crest and on its seaward slope. The OBS data have been analyzed with the objective of determining the velocity structure in the upper portion of the accretionary wedge especially the hydrate stability zone and underlying free gas. As identified by a clear refracted phase, the velocity structure above the BSR shows anomalous high velocities of about 1.95 (0.5) km/s at shallow depths of 80 - 110 m. On vertical incidence data, high amplitude reflectors are observed near this depth. Below the BSR, the velocities increase to -2.4 km/s at sub-seafloor depths of about 600 m. A strong refracted phase with a velocity of 4.0 km/s is generated at a depth of about 1700 mbsf. Velocities from traveltime inversion of OBS data are in general agreement with the Integrated Ocean Drilling Program (IODP) X311 downhole sonic velocities. In particular, on the log data, a layer with low porosity and high velocities of 2.4 - 2.8 km/s was observed at depths of 50 - 75 m. This probably corresponds with the 1.95 km/s layer at depths of 80-110 m interpreted from the OBS data. The refraction data thus suggest that this high-velocity layer varies laterally through the frontal ridge region, out to distances of at least 4 km from the drillhole. BSR depths (250-280 m) estimated in the present work also agree with the IODP X311 depths. From the velocity structure, we can make estimates of hydrate concentration in a region clo.
Download or read book Seismic Structure Gas Hydrate and Slumping Studies on the Northern Cascadia Margin Using Multiple Migration and Full Waveform Inversion of OBS and MCS Data written by Subbarao Yelisetti and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary focus of this thesis is to examine the detailed seismic structure of the northern Cascadia margin, including the Cascadia basin, the deformation front and the continental shelf. The results of this study are contributing towards understanding sediment deformation and tectonics on this margin. They also have important implications for exploration of hydrocarbons (oil and gas) and natural hazards (submarine landslides, earthquakes, tsunamis, and climate change). The first part of this thesis focuses on the role of gas hydrate in slope failure observed from multibeam bathymetry data on a frontal ridge near the deformation front off Vancouver Island margin using active-source ocean bottom seismometer (OBS) data collected in 2010. Volume estimates (? 0.33 km^3) of the slides observed on this margin indicate that these are capable of generating large (? 1 ? 2 m) tsunamis. Velocity models from travel time inversion of wide angle reflections and refractions recorded on OBSs and vertical incidence single channel seismic (SCS) data were used to estimate gas hydrate concentrations using effective medium modeling. Results indicate a shallow high velocity hydrate layer with a velocity of 2.0 ? 2.1 km/s that corresponds to a hydrate concentration of 40% at a depth of 100 m, and a bottom simulating reflector (BSR) at a depth of 265 ? 275 m beneath the seafloor (mbsf).These are comparable to drilling results on an adjacent frontal ridge. Margin perpendicular normal faults that extend down to BSR depth were also observed on SCS and bathymetric data, two of which coincide with the sidewalls of the slump indicating that the lateral extent of the slump is controlled by these faults. Analysis of bathymetric data indicates, for the first time, that the glide plane occurs at the same depth as the shallow high velocity layer (100?10 mbsf). In contrast, the glide plane coincides with the depth of the BSR on an adjacent frontal ridge ... .
Download or read book Seismic Characterization of Marin Gas Hydrates and Free Gas at Northern Hydrate Ridge Cascadia Margin written by Carl Jörg Petersen and published by . This book was released on 2004 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract ; Zs.-Fassung.
Download or read book World Atlas of Submarine Gas Hydrates in Continental Margins written by Jürgen Mienert and published by Springer Nature. This book was released on 2022-01-01 with total page 515 pages. Available in PDF, EPUB and Kindle. Book excerpt: This world atlas presents a comprehensive overview of the gas-hydrate systems of our planet with contributions from esteemed international researchers from academia, governmental institutions and hydrocarbon industries. The book illustrates, describes and discusses gas hydrate systems, their geophysical evidence and their future prospects for climate change and continental margin geohazards from passive to active margins. This includes passive volcanic to non-volcanic margins including glaciated and non-glaciated margins from high to low latitudes. Shallow submarine gas hydrates allow a glimpse into the past from the Last Glacial Maximum (LGM) to modern environmental conditions to predict potential changes in future stability conditions while deep submarine gas hydrates remained more stable. This demonstrates their potential for rapid reactions for some gas hydrate provinces to a warming world, as well as helping to identify future prospects for environmental research. Three-dimensional and high-resolution seismic imaging technologies provide new insights into fluid flow systems in continental margins, enabling the identification of gas and gas escape routes to the seabed within gas hydrate environments, where seabed habitats may flourish. The volume contains a method section detailing the seismic imaging and logging while drilling techniques used to characterize gas hydrates and related dynamic processes in the sub seabed. This book is unique, as it goes well beyond the geophysical monograph series of natural gas hydrates and textbooks on marine geophysics. It also emphasizes the potential for gas hydrate research across a variety of disciplines. Observations of bottom simulating reflectors (BSRs) in 2D and 3D seismic reflection data combined with velocity analysis, electromagnetic investigations and gas-hydrate stability zone (GHSZ) modelling, provide the necessary insights for academic interests and hydrocarbon industries to understand the potential extent and volume of gas hydrates in a wide range of tectonic settings of continental margins. Gas hydrates control the largest and most dynamic reservoir of global carbon. Especially 4D, 3D seismic but also 2D seismic data provide compelling sub-seabed images of their dynamical behavior. Sub-seabed imaging techniques increase our understanding of the controlling mechanisms for the distribution and migration of gas before it enters the gas-hydrate stability zone. As methane hydrate stability depends mainly on pressure, temperature, gas composition and pore water chemistry, gas hydrates are usually found in ocean margin settings where water depth is more than 300 m and gas migrates upward from deeper geological formations. This highly dynamic environment may precondition the stability of continental slopes as evidenced by geohazards and gas expelled from the sea floor. This book provides new insights into variations in the character and existence of gas hydrates and BSRs in various geological environments, as well as their dynamics. The potentially dynamic behavior of this natural carbon system in a warming world, its current and future impacts on a variety of Earth environments can now be adequately evaluated by using the information provided in the world atlas. This book is relevant for students, researchers, governmental agencies and oil and gas professionals. Some familiarity with seismic data and some basic understanding of geology and tectonics are recommended.
Download or read book Mound and Vent Structures Associated with Gas Hydrates Offshore Vancouver Island Analysis of Single channel and Deep towed Multichannel Seismic Data written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The study focuses mainly on two gas hydrate-related targets, located on the Northern Cascadia Margin, offshore Vancouver Island: (1) a recently identified 70-80-m high carbonate mound, Cucumber Ridge, located ~3.5-km west of Ocean Drilling Program (ODP) Site 889 and Integrated Ocean Drilling Program (IODP) Site U1327, and (2) a large cold vent, Bullseye vent, which is up to ~500 m in diameter and was drilled by IODP at Site U1328. The objective of this thesis is to analyze seismic data that provide indicators of locally focused fluid flow and characteristics of the gas hydrate occurrence associated with these two features. A grid of closely-spaced single channel seismic (SCS) data was collected at Cucumber Ridge in July/August 2001, and deep-towed multichannel seismic (MCS) lines were collected using Deep-towed Acoustics and Geophysics System (DTAGS) at the Bullseye vent area and at Cucumber Ridge in October 2002. The high-resolution SCS data, with a frequency bandpass of 40-150 Hz, recorded coherent reflectivity down to about 400 m beneath the seafloor, and provide excellent images of the subseafloor structure of Cucumber Ridge and of the gas hydrate bottom-simulating reflector (BSR) beneath it. Cucumber Ridge is interpreted to have developed as a structural topographic high in the hanging wall of a large reverse fault formed at the base of the current seaward slope. The fault zone provides pathways for fluids including gas to migrate to the seafloor where diagenetic carbonate forms and cements the near-surface sediments. Over the seismic grid, heat flow was derived from the depth of the BSR. A simple 2-D analytical correction for theoretical heat flow variations due to topography is applied to the data. Across the mound, most of the variability in heat flow is explained by topographic effects, including a local 6 mW/m2 negative anomaly over the central mound and a large 20 mW/m2 positive anomaly over the mound steep side slope. However, just south of the mound, th.
Download or read book Deformation Fluid Venting and Slope Failure at an Active Margin Gas Hydrate Province Hydrate Ridge Cascadia Accretionary Wedge written by Joel E. Johnson and published by . This book was released on 2004 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the last 15 years, numerous geophysical surveys and geological sampling and coring expeditions have helped to characterize the tectonic setting, subsurface stratigraphy, and gas hydrate occurrence and abundance within the region of the accretionary wedge surrounding Hydrate Ridge. Because of these investigations, Hydrate Ridge has developed as an international site of active margin gas hydrate research. The manuscripts presented in this dissertation are focused on the geologic setting hosting the gas hydrate system on Hydrate Ridge. These papers examine how active margin tectonic processes influence both the spatial and temporal behavior of the gas hydrate system at Hydrate Ridge and likely across the margin. From a high resolution sidescan sonar survey (Chapter II) collected across the region, the distribution of high backscatter, as well as the locations of mud volcanoes and pockmarks indicates variations in the intensity and activity of fluid flow across the Hydrate Ridge region. Coupled with subsurface structural mapping, the origins for many of these features as well the locations of abundant gas hydrates can be linked to folds within the subsurface. Continued structural mapping, coupled with age constraints of the subsurface stratigraphy from ODP drilling, resulted in a model for the construction of the accretionary wedge within the Hydrate Ridge region (Chapter III). This model suggests the wedge advanced in three phases of growth since the late Pliocene and was significantly influenced by the deposition of the Astoria fan on the abyssal plain and left lateral strike slip faulting. Changes in structural vergence, documented here, also help explain the variability in bathymetric relief across the region. Determination of the occurrence and timing of Holocene slope failures derived from Hydrate Ridge (Chapter IV) and comparison with a Holocene marine record of Cascadia subduction zone earthquakes suggests earthquake induced slope failure within the gas hydrate stability zone does occur at Hydrate Ridge and thus, may represent a high frequency mechanism for the mobilization of seafloor and subseafloor gas hydrates across the margin.
Download or read book Geological Survey of Canada Open File 6552 written by and published by Natural Resources Canada. This book was released on with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Seismic Characterisation of Hydrate and Shallow Gas Systems Associated with Active Margin Sediments and Structures in the Pegasus Basin Hikurangi Margin New Zealand written by Douglas Ross Allan Fraser and published by . This book was released on 2017 with total page 289 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Pegasus Basin off the east coast of New Zealand's North Island is a frontier basin that hosts a large gas hydrate province. The basin has a large amount of faulting, which has lead to the creation of many interesting and unique accumulations of gas hydrates. In 2009/2010, petroleum industry standard 2D seismic data were acquired across the basin by New Zealand Petroleum and Minerals (a New Zealand government agency) to generate interest in exploration of this basin for conventional oil and gas. This seismic data set presents an unique opportunity to examine the basin's gas hydrate systems with the aim of determining the economic potential of the gas hydrates in the basin while improving our understanding of how observed gas hydrate features were formed. The seismic data were reprocessed to optimise the imaging of features related to gas hydrates. When the data were examined, there were numerous gas hydrate features found, so only a selection are presented in this thesis. With the assistance of seismic attributes, Bottom Simulating Reflections (BSRs) and blanking zones are examined. High-density velocity analysis is used to characterize areas of hydrate (higher velocity) and free gas (lower velocity). The high-density velocity analysis proved to be a very effective technique for examining the structure of gas migration chimneys. Two of the most interesting features identified in the data set include a blank dome shape with a gas chimney at its centre and a text book hydrate/free gas phase reversal that is examined in detail using amplitude vs offset (AVO) and inversion analysis techniques. The model for fluid flow and how the free gas from a chimney at the centre of the blanking zone is converted to hydrate is discussed. The hydrate and free gas phase reversal that is observed was formed by localised fluid flowing from depth into the gas hydrate stability zone (GHSZ). As the BSR becomes shallower, the sea floor deepens at this location. Without a localised fluid flow, the BSR would increase in depth with the increasing depth of the sea floor. Gas hydrate saturation and volumetric analyses were performed for one target. Concentrations were determined using empirical saturation formulae, confirming a potential target. The question of how much gas hydrate potentially is present in the basin, is discussed based both my work and that of others.
Download or read book 3 D Travel Time Tomography of the Gas Hydrate Area Offshore Vancouver Island Based on OBS Data written by Mikhail Mikhailovich Zykov and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Subaqueous Mass Movements and Their Consequences written by D.G. Lintern and published by Geological Society of London. This book was released on 2019-09-25 with total page 597 pages. Available in PDF, EPUB and Kindle. Book excerpt: The challenges facing submarine mass movement researchers and engineers are plentiful and exciting. This book follows several high-profile submarine landslide disasters that have reached the world’s attention over the past few years. For decades, researchers have been mapping the world’s mass movements. Their significant impacts on the Earth by distributing sediment on phenomenal scales is undeniable. Their importance in the origins of buried resources has long been understood. Their hazard potential ranges from damaging to apocalyptic, frequently damaging local infrastructure and sometimes devastating whole coastlines. Moving beyond mapping advances, the subaqueous mass movement scientists and practitioners are now also focussed on assessing the consequences of mass movements, and the measurement and modelling of events, hazard analysis and mitigation. Many state-of-the-art examples are provided in this book, which is produced under the auspices of the United Nations Educational, Scientific and Cultural Organisation Program S4SLIDE (Significance of Modern and Ancient Submarine Slope LandSLIDEs).
Download or read book The Lifetime of Methane Bubbles Through Sediment and Water Column written by Regina Katsman and published by Frontiers Media SA. This book was released on 2022-09-21 with total page 239 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Petroleum Abstracts written by and published by . This book was released on 1993 with total page 1752 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings of the Ocean Drilling Program written by Ocean Drilling Program and published by . This book was released on 1994 with total page 746 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Canadian Journal of Earth Sciences written by and published by . This book was released on 2015 with total page 502 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Interaction of Fluid Flow and Accretion related Deformation of Cascadia Basin Sediment written by Guy Robert Cochrane and published by . This book was released on 1994 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Ocean Margin Systems written by Gerold Wefer and published by Springer. This book was released on 2014-03-12 with total page 495 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean margins are the transitional zones between the oceans and continents. They represent dynamic systems in which numerous processes shape the environment and result in impacting the utilization and hazard potentials for humans. These processes are influenced by a variety of steering mechanisms, from mountain building and climate on the land to tectonics and sea-level fluctuations in ocean margins. This book examines various aspects of regulation for the long-term development of ocean margins, of the impact of fluids and of the dynamics of benthic life at and below the seafloor in ocean margin systems.
