A B S T R A C TMost seismic processing algorithms generally consider the sea surface as a flat reflector. However, acquisition of marine seismic data often takes place in weather conditions where this approximation is inaccurate. The distortion in the seismic wavelet introduced by the rough sea may influence (for example) deghosting results, as deghosting operators are typically recursive and sensitive to the changes in the seismic signal. In this paper, we study the effect of sea surface roughness on conventional (5-160 Hz) and ultra-high-resolution (200-3500 Hz) single-component towed-streamer data. To this end, we numerically simulate reflections from a rough sea surface using the Kirchhoff approximation. Our modelling demonstrates that for conventional seismic frequency band sea roughness can distort results of standard one-dimensional and two-dimensional deterministic deghosting. To mitigate this effect, we introduce regularisation and optimisation based on the minimum-energy criterion and show that this improves the processing output significantly. Analysis of ultra-high-resolution field data in conjunction with modelling shows that even relatively calm sea state (i.e., 15 cm wave height) introduces significant changes in the seismic signal for ultra-high-frequency band. These changes in amplitude and arrival time may degrade the results of deghosting. Using the field dataset, we show how the minimum-energy optimisation of deghosting parameters improves the processing result.
Here, we present new results from seismic, geological, and geochemical studies conducted in 2015–2019 in the Petrozavodsk Bay of Lake Onego, NW Russia. The aims of these investigations were to (i) to characterize the structure of Quaternary deposits and (ii) provide new evidence of modern geodynamic movements and gas-seepage in Holocene sediments. The structure of the recovered deposits was composed of lacustrine mud, silt and sands from the Holocene, limno-glacial clays (varved clays) from the Late Glacial–Interglacial Transition, and glacial deposits (till) from the Late Pleistocene. The thickness of these deposits varied in different parts of the bay. Many pockmarks created by gases escaping and reaching sediment-water interface were observed in these deposits. Such pockmarks can play a significant role in the geochemical and biological processes in the bottom sediment surface, and gases that escape might modify the physicochemical characteristics of the environment.
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