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181.
2004年9月17日02时31分广东省阳江市发生MS 4.9级地震,造成14个镇的57个行政村共1620多间房屋(主要为老旧民房)遭受轻微破坏,受影响居民21195户,经济损失2300多万元。震后进行了地震影响场调查,绘制了这次地震的等震线分布图,并对其发震构造进行了分析探讨。 相似文献
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Seismic images of a collision zone offshore NW Sabah/Borneo 总被引:2,自引:0,他引:2
Dieter Franke Udo Barckhausen Ingo Heyde Mark Tingay Nordin Ramli 《Marine and Petroleum Geology》2008,25(7):606-624
Multichannel reflection seismic data from the southern South China Sea, refraction and gravity modelling were used to investigate the compressional sedimentary structures of the collision-prone continental margin off NW Borneo. An elongated imbricate deepwater fan, the toe Thrust Zone bounds the Northwest Borneo Trough to the southeast. The faults separating the individual imbricates cut through post-Early Miocene sediments and curve down to a carbonate platform at the top of the subsiding continental Dangerous Grounds platform that forms the major detachment surface. The age of deformation migrates outward toward the front of the wedge. We propose crustal shortening mechanisms as the main reason for the formation of the imbricate fan. At the location of the in the past defined Lower Tertiary Thrust Sheet tectonostratigraphic province a high velocity body was found but with a much smaller extend than the previously defined structure. The high velocity structure may be interpreted either as carbonates that limit the transfer of seismic energy into the sedimentary layers beneath or as Paleogene Crocker sediments dissected by remnants of a proto-South China Sea oceanic crust that were overthrust onto a southward migrating attenuated continental block of the Dangerous Grounds during plate convergence. 相似文献
184.
Mud volcanoes recently discovered on the offshore Calabrian Arc are investigated at two sites 60 km apart, in water depths of 1650--2300 m, using swath bathymetry, 2D&3D multichannel seismic and cores. The seabed and subsurface data provide information on their formation and functioning in relation to tectonic activity during the rapid Plio-Quaternary advance of the accretionary prism. Fore-arc extension and thrust-belt compression are seen to have involved two main phases of activity, separated by a regional unconformity recording a mid-Pliocene (3.5–3.0 Ma) tectonic reorganization. The two sites of mud volcanism lie in contrasting tectonic settings (inner fore-arc basin vs central fold-and-thrust belt) and record differing forms of seabed extrusive activity (twin mud cones and a caldera vs a broad mud pie). At both sites, subsurface data show that mud volcanism took place throughout the second tectonic phase, since the late Pliocene; differing forms of mud extrusion were accompanied by subsidence to form depressions beneath and within extrusive edifices up to 1.5 km thick. The basal subsidence depressions point to sources within the succession of thrusts underlying the inner to central Arc, consistent with microfossils within cored mud breccias from both sites that are derived from strata as old as Late Cretaceous. 相似文献
185.
TCP Westwood(TCPW)和Vegas都是基于测量的TCP New-Reno增强算法。TCPW针对ACK流直接估算可用带宽,在慢启动和线性递增部分依然采用传统Reno的盲目递增的机制,导致发送端较为频繁的重传。对这几种算法原理进行分析阐述,并提出1种改进方法,更精确的测量估计带宽,通过网络仿真工具NS2进行验证,明显去除TCP全局同步现象,增强网络性能。 相似文献
186.
为了理解地震的发生和地壳结构不均匀性的关系,利用南加州地震台网的固定台和临时台所记录的2863个兰德斯余震和区域地震,共计107401个P波和19624个S波高质量的到时数据,采用地震层析成像方法得到了兰德斯地震区P波和S波的精细的三维速度结构和泊松比分布.结果显示,地震的发生和分布与地壳结构的横向不均匀性有密切的关系.总体上看,兰德斯地震区余震成丛分布,并被低速块体截断,其中4级以上地震大多分布于P波高、低速异常过渡区域或偏向高速块体一侧,这可能是因为高速区多属地壳脆性介质,易于造成应力集中,导致地震;反之,低速度区则可能代表破碎程度较高、富含流体或温度较高区域,因而更倾向于产生无震变形.基于兰德斯地震区强震震源位置、地震区P波、S波速度异常与泊松比分布推断,兰德斯地震区可能有流体存在.地壳流体易使地壳岩石弱化,从而引发大地震. 相似文献
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The Campos, Santos and Pelotas basins have been investigated in terms of 2D seismo-stratigraphy and subsidence. The processes controlling accommodation space (e.g. eustacy, subsidence, sediment input) and the evolution of the three basins are discussed. Depositional seismic sequences in the syn-rift Barremian to the drift Holocene basin fill have been identified. In addition, the subsidence/uplift history has been numerically modeled including (i) sediment flux, (ii) sedimentary basin framework, (iii) relation to plate-tectonic reconfigurations, and (iv) mechanism of crustal extension. Although the initial rift development of the three basins is very similar, basin architecture, sedimentary infill and distribution differ considerably during the syn-rift sag to the drift basin stages. After widespread late Aptian–early Albian salt and carbonate deposition, shelf retrogradation dominated in the Campos Basin, whereas shelf progradation occurred in the Santos Basin. In the Tertiary, these basin fill styles were reversed: since the Paleogene, shelf progradation in the Campos Basin contrasts with overall retrogradation in the Santos Basin. In contrast, long-term Cretaceous–Paleogene shelf retrogradation and intense Neogene progradation characterize the Pelotas Basin. Its specific basin fill and architecture mainly resulted from the absence of salt deposition and deformation. These temporally and spatially varying successions were controlled by specific long-term subsidence/uplift trends. Onshore and offshore tectonism in the Campos and Santos basins affected the sediment flux history, distribution of the main depocenters and occurrence of hydrocarbon stratigraphic–structural traps. This is highlighted by the exhumation and erosion of the Serra do Mar, Serra da Mantiqueira and Ponta Grossa Arch in the hinterland, as well as salt tectonics in the offshore domain. The Pelotas Basin was less affected by changes in structural regimes until the Eocene, when the Andean orogeny caused uplift of the source areas. Flexural loading largely controlled its development and potential hydrocarbon traps are mainly stratigraphic. 相似文献
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190.