One of the problems experienced in marine geophysical exploration is that the layered features in the migration imaging profile are blurred and the seismic energy reflected is weaker in the middle or lower parts. In t...One of the problems experienced in marine geophysical exploration is that the layered features in the migration imaging profile are blurred and the seismic energy reflected is weaker in the middle or lower parts. In this study we model the seismic wavefield records in the undulating seafloor when there is both a slight change and significant change in seafloor topography to analyze its influence on the seismic reflection data and migration imaging profiles. We compare and analyze the wave field records collected at the same point on the original and modified velocity models, and the cross-bonding resulting migration imaging profiles. The results show that whether the seismic reflection data collection is performed along the direction of the survey line or against the direction of the survey line, slight changes in the seafloor topography have little effect on the wave field records and the migration profile, while significant changes in the seafloor topography have great effect on both the wave field records and migration profile.展开更多
The crustal basement of Northwest Germany can be interpreted as an “Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and SW-NE (Rhenish) running horst and graben system. In Late Devonian and E...The crustal basement of Northwest Germany can be interpreted as an “Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and SW-NE (Rhenish) running horst and graben system. In Late Devonian and Early Carboniferous times, this assemblage was flooded by the sea and mainly marine carbonates were deposited on the horsts and Stillwater shales in the grabens, as interpretable through magnetotelluric measurements. Dur</span><span style="font-family:Verdana;">ing the Late Carboniferous Variscan Orogeny, this terrain became the </span><span style="font-family:Verdana;">coal-rich </span><span style="font-family:Verdana;">foreland of the colliding Rhenohercynian belt. The shale-filled grabens </span><span style="font-family:Verdana;">reacted </span><span style="font-family:Verdana;">through folding and thrusting with different anticlinal patterns, the main</span><span style="font-family:Verdana;"> carbonate covered horst in a still unknown way. This horst was the location of the Late Carboniferous basin center and of the inverted oil-rich Mesozoic Lower Saxony Basin (southwestern sector), respectively, with the so-called Bramsche Massif therein. It probably acted as an indenter for the evolution of the Variscan ore-rich Harz Mountains and forced the approaching Rhenohercynian orogen to stack the appropriate tectonic nappes by horizontal shortening to very high altitudes and the root into large depths. Based on seismic evidence this root is still an uncompleted crust/mantle transition zone with a deep reflection seismic and petrological Moho and a shallower hardly reflecting refraction seismic velocity Moho. The alternative, partly unsolved location of the Variscan Deformation Front in Northwest Germany may represent the new findings. The results may be supported by a comparison with features of the northern Alpine deformation belt.展开更多
Based on seismic tomography, explosive seismic sounding and seismic reflective profiling data, the lithosphere of the Qinling orogen can be divided into three parts. The upper lithosphere is the crust, having a thickn...Based on seismic tomography, explosive seismic sounding and seismic reflective profiling data, the lithosphere of the Qinling orogen can be divided into three parts. The upper lithosphere is the crust, having a thickness of 32-34km. The middle lithosphere is horizontal layering. 25-40 km thick. The lower lithosphere juxtaposed steeply declined high velocity and low velocity rock series, which might be split open under extension. Hot mantle flow upwelled to the level of the Moho then turned to horizontal direction and formed middle lithosphere. The shape of these kinds of lithosphere is somewhat like mushroom cloud in nuclear explosion. There is no causality between crustal structure of the Qinling orogen and its upper mantle structure nowadays. The Qinling orogen might be an intracontinental orogen of Indosinian-Yanshanian period, formed by wedging of the Yangtze crust into the middle crust of North China craton. and by reformation of extension in E-W direction in postorogenic period.展开更多
基金The National Natural Science Foundation of China under contract Nos 41504084 and 41274120
文摘One of the problems experienced in marine geophysical exploration is that the layered features in the migration imaging profile are blurred and the seismic energy reflected is weaker in the middle or lower parts. In this study we model the seismic wavefield records in the undulating seafloor when there is both a slight change and significant change in seafloor topography to analyze its influence on the seismic reflection data and migration imaging profiles. We compare and analyze the wave field records collected at the same point on the original and modified velocity models, and the cross-bonding resulting migration imaging profiles. The results show that whether the seismic reflection data collection is performed along the direction of the survey line or against the direction of the survey line, slight changes in the seafloor topography have little effect on the wave field records and the migration profile, while significant changes in the seafloor topography have great effect on both the wave field records and migration profile.
文摘The crustal basement of Northwest Germany can be interpreted as an “Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and SW-NE (Rhenish) running horst and graben system. In Late Devonian and Early Carboniferous times, this assemblage was flooded by the sea and mainly marine carbonates were deposited on the horsts and Stillwater shales in the grabens, as interpretable through magnetotelluric measurements. Dur</span><span style="font-family:Verdana;">ing the Late Carboniferous Variscan Orogeny, this terrain became the </span><span style="font-family:Verdana;">coal-rich </span><span style="font-family:Verdana;">foreland of the colliding Rhenohercynian belt. The shale-filled grabens </span><span style="font-family:Verdana;">reacted </span><span style="font-family:Verdana;">through folding and thrusting with different anticlinal patterns, the main</span><span style="font-family:Verdana;"> carbonate covered horst in a still unknown way. This horst was the location of the Late Carboniferous basin center and of the inverted oil-rich Mesozoic Lower Saxony Basin (southwestern sector), respectively, with the so-called Bramsche Massif therein. It probably acted as an indenter for the evolution of the Variscan ore-rich Harz Mountains and forced the approaching Rhenohercynian orogen to stack the appropriate tectonic nappes by horizontal shortening to very high altitudes and the root into large depths. Based on seismic evidence this root is still an uncompleted crust/mantle transition zone with a deep reflection seismic and petrological Moho and a shallower hardly reflecting refraction seismic velocity Moho. The alternative, partly unsolved location of the Variscan Deformation Front in Northwest Germany may represent the new findings. The results may be supported by a comparison with features of the northern Alpine deformation belt.
基金Project supported by the National Natural Science Foundation of China.
文摘Based on seismic tomography, explosive seismic sounding and seismic reflective profiling data, the lithosphere of the Qinling orogen can be divided into three parts. The upper lithosphere is the crust, having a thickness of 32-34km. The middle lithosphere is horizontal layering. 25-40 km thick. The lower lithosphere juxtaposed steeply declined high velocity and low velocity rock series, which might be split open under extension. Hot mantle flow upwelled to the level of the Moho then turned to horizontal direction and formed middle lithosphere. The shape of these kinds of lithosphere is somewhat like mushroom cloud in nuclear explosion. There is no causality between crustal structure of the Qinling orogen and its upper mantle structure nowadays. The Qinling orogen might be an intracontinental orogen of Indosinian-Yanshanian period, formed by wedging of the Yangtze crust into the middle crust of North China craton. and by reformation of extension in E-W direction in postorogenic period.
