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91.
Offset continuation (OCO) is a seismic configuration transform designed to simulate a seismic section as if obtained with
a certain source-receiver offset using the data measured with another offset. Since OCO is dependent on the velocity model
used in the process, comparison of the simulated section to an acquired section allows for the extraction of velocity information.
An algorithm for such a horizon-oriented velocity analysis is based on so-called OCO rays. These OCO rays describe the output
point of an OCO as a function of the Root Mean Square (RMS) velocity. The intersection point of an OCO ray with the picked
traveltime curve in the acquired data corresponding to the output half-offset defines the RMS velocity at that position. We
theoretically relate the OCO rays to the kinematic properties of OCO image waves that describe the continuous transformation
of the common-offset reflection event from one offset to another. By applying the method of characteristics to the OCO image-wave
equation, we obtain a raytracing-like procedure that allows to construct OCO trajectories describing the position of the OCO
output point under varying offset. The endpoints of these OCO trajectories for a single input point and different values of
the RMS velocity form then the OCO rays. A numerical example demonstrates that the developed ray-tracing procedure leads to
reliable OCO rays, which in turn provide high-quality RMS velocities. The proposed procedure can be carried out fully automatically,
while conventional velocity analysis needs human intervention. Moreover, since velocities are extracted using offset sections,
more redundancy is available or, alternatively, OCO velocities can be studied as a function of offset. 相似文献
92.
F. A. Temporim Ricardo Ivan Ferreirae da Trindade Marcos Egydio-Silva Tiago Valim Angelo Eric Tohver Caroline Cibele Soares Lucas Pequeno Gouvêa Julio Cesar Mendes Silvia Regina Medeiros Antônio Carlos Pedrosa-Soares Gabriel Gomes Silva 《地学学报》2023,35(1):23-31
Featuring 3 000-km-long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (~500 Ma) post-collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep-seated intrusions, ellipsoidal-shaped roots with gabbroic-to-hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE-trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith-size bodies of coarse-grained granite emplaced at the shallow to mid-crust, show general NS-trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice. 相似文献
93.
Camila Rodrigues Costa Cynthia Fernandes Pinto da Luz Ingrid Horák-Terra Plínio Barbosa de Camargo Uidemar Morais Barral Carlos Victor Mendonça-Filho Thamyres Sabrina Gonçalves Alexandre Christófaro Silva 《第四纪科学杂志》2023,38(1):61-75
The Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central-eastern Brazil. A multi-proxy approach was used that involved palynological analysis, stable isotopes (δ13C, δ15N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub-humid climatic conditions seem to have been established in the mid-/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc. 相似文献