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Geology
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
The Sunda Shelf consists of stretched continental crust consisting of grabens in the basement rocks overlain by sediment. The continental slope is narrow and steep, and has a water depth that ranges from 200 to 1000 m. In contrast, the oceanic crust extends from water depths of approximately 3000 to over 5000 m. The ocean floor depth in most active marginal basins is similar to spreading ocean-ridge systems. Seismic surveys and gravity inversion data of the SCS indicate that the depth to the Moho (crustal thickness) varies from 30 km in the Sunda Shelf to 7 km in the oceanic crust. Dredged rocks in marginal basins have the same geochemistry of either major or minor elements as spreading ridge systems. The marginal basin crust is young based on both direct and indirect evidence: amount of sediment cover, geologic trends, paleomagnetic studies, and fit of predrift continental margins.
The Geoid and Geophysical Prospecting
Published in Petr Vaníček, Nikolaos T. Christou, GEOID and Its GEOPHYSICAL INTERPRETATIONS, 2020
Exploration for oil and gas in water depths of several hundred and even thousands of meters has gained increased interest as more and more shallow water areas have become mature exploration areas. The reasons for a special section dealing with the ocean-continent boundary are the gravity and sea surface anomalies associated with the rapidly increasing water depth as one moves from the shelf into the abyssal plain. The undulations of the sea surface over a typical passive margin, with water depths increasing from a few tens of meters to more than 5 km, is usually in the order of 5 to 6 m. Over a distance of about 80 km, this is approximately equivalent to some 100 mgal. An adjustment for the topographic effects alone will drastically over-compensate the geoid. This is caused by the isostatic compensation. Corrections for isostatic compensation can be performed in different ways. The principles of isostacy in the oceanic lithosphere are discussed in other chapters of this book especially in Chapter 10.
Stratigraphy and Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
With a rise in sea-level, the sea transgressed on the shelf. Two situations arose depending on the relative rates of subsidence and sedimentation. When the rate of sea-level rise was slow, sediments blanketed the shelf, covering the previously incised river valleys. The terrigenous sediment load was deposited mainly in the coastal deltas and sediment supply to submarine fans slowed down. This stage has been named the Transgressive Systems Tract (TST). When the sea level was high and the sediment supply was also large, the coastal plain prograded across the shelf. The thick alluvial and deltaic complex developed at this stage constituted what has been named a Highstand Systems Tract or HST (see Fig. 8.16B). The well-known post-glacial delta lobes of the Mississippi River (Fig. 6.31) are cited as examples of High- and Lowstand Systems Tracts. The first three of these lobes represent the transgressive systems tract. The others are highstand systems tracts (Kolb and Van Lopik 1966, see also Fig. 6.31). Each of these lobes represent a parasequence (Miall 1984), which, as defined by seismic stratigraphers, is ‘a relatively conformable succession of genetically related beds or bedsets bounded by marine flooding surfaces and their correlative surfaces. Parasequences are progradational and therefore the beds within parasequences shoal upward’ (Van Wagoner et al. 1990). (A) Lowstand Systems Tract (LST) and (B) Highstand Systems Tract (HST) produced respectively by sea-level fall and rise. Note the timing of the model with respect to the sea-level sine curve (modified and redrawn after Posamentier et al. 1988).
Investigating the Effects of Climate Change on Structural Actions
Published in Structural Engineering International, 2022
André Orcesi, Alan O’Connor, Dimitris Diamantidis, Miroslav Sykora, Teng Wu, Mitsuyoshi Akiyama, Abdul Kadir Alhamid, Franziska Schmidt, Maria Pregnolato, Yue Li, Babak Salarieh, Abdullahi M. Salman, Emilio Bastidas-Arteaga, Olga Markogiannaki, Franck Schoefs
The complete framework for probabilistic sea-level rise hazard assessments has been presented by Ref. [107] First, the regional sea-level rise, defined as the sea-level rise in a particular location in the ocean, is estimated by multiplying each global mean sea-level rise component (i.e. the average value of sea-level rise over the ocean) with its corresponding spatial variability (hereafter referred to as sea-level fingerprint).105 Three sea-level rise components are considered herein: (1) sterodynamic sea-level rise due to thermal expansion and dynamical ocean currents; (2) glacier sea-level rise due to surface mass balance; and (3) ice sheet sea-level rise due to dynamical ice shelf basal melting. The surface mass balance represents the net loss of snow accumulation and ice mass melting of the glacier and ice sheet, while the dynamical ice shelf basal melting is caused by the detachment of the ice shelf from the bedrock due to ocean warming, which accelerates the ice sheet flow into the ocean. To generate a more representative outcome, further study is needed to consider other non-climatic sea-level rise components including tectonics and glacial isostatic adjustment.
Marine Geology and Sand Resources of the Southern North Carolina Inner Shelf
Published in Marine Georesources & Geotechnology, 2022
Ian Conery, John P. Walsh, David Mallinson, David R. Corbett
Widespread surveying has been conducted in northern NC (e.g., Thieler et al. 2014; NCDCM 2016), but there was a lack of broad-scale data coverage in the southern NC OCS as work has been conducted primarily in NC State waters (0-3 mi). To address this deficiency, reconnaissance sub-bottom geophysical data and vibracores were collected in 2015 based on data coverage gaps, as part of the Atlantic Sand Assessment Project, a post-Sandy BOEM-funded sand resource assessment effort (Walsh, Conery, Mallinson, et al. 2016). The work herein stems from this project, and specific objectives are to: 1) examine the geomorphology and geology of the southern NC shelf, 2) evaluate the distribution of sand resources offshore southern NC and its relationship to geologic context, and 3) assess the variability in form and classification of paleochannels and hardbottom.
A methodology to derive design metocean internal wave current criteria for submarine structures
Published in Ships and Offshore Structures, 2022
Liaqat Ali, Yong Bai, Yuxin Xu
The barotropic part of the vertically integrated body force is obtained by the combination of tidal flow and bathymetry and it is given by . Only the semidiurnal solar and the semidiurnal lunar components that lead to the 14-day period in tidal amplitude are considered. A first indication of the preferred locations for the generation of internal tides is given by the barotropic forcing. The flow conservation on the slopes implies that H is conserved from the deep sea abyssal plain to the shelf. The barotropic forcing is proportional to . Therefore, the term is not necessarily maximum at the steepest part of the slope, but generally very close to the top of the slope.