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南海海槽是全球大地震发生频率最高的地区之一,该地区增生楔上斜坡盆地内的重力流沉积记录了多分支断层及大地震活动历史.利用国际综合大洋钻探计划(IODP)314-316航次岩心-地震-综合测井资料,在详细分析南海海槽增生楔上斜坡盆地内重力流沉积特征基础上,阐明了其对多分支断层和大地震活动的响应机制.研究结果表明,南海海槽增生楔上斜坡盆地内依次充填了楔形块体流、峡谷和表层块体流沉积:楔形块体流形成于多分支断层活动早期,表现出北厚南薄的楔形特征,反映了多分支断层的持续活动的特征,沉积物中富含的粗颗粒泥质角砾岩反映了早期多分支断层剧烈活动的特征;峡谷系统由密集峡谷,大型块体流和轴向峡谷组成,主要受到多分支断层耦合造成斜坡变陡、区域地层孔隙流体压力增大和盆地不均衡抬升的影响;表层块体流位于盆地顶部,由多期次弱振幅块体流叠加组成,现今海底表面表现为大量“马蹄形”的垮塌地形,这些相对短期内广泛分布的块体流应该是由地震引起的地表震动触发的.斜坡盆地内重力流沉积特征反映了多分支断层活动历史以及大地震的发生过程:即1.95~1.55Ma,多分支断层形成初期活动剧烈,逆冲活动造成了断层上盘沉积物垮塌,楔形块体流沉积在斜坡盆地底部;1.55~1.07Ma,多分支断层西部耦合,导致斜坡盆地出现东高西低的构造格局以及盆地西部区域楔体和断层处能量的集聚;1.07Ma至今,断层处能量间断释放,引发多次大地震.
The South China Sea Trough is one of the areas with the highest frequency of earthquakes in the world, and the gravitational flow sedimentation in the upwelling wedge upper slope basin records the history of multi-branch faults and large earthquakes. Using the International Integrated Ocean Drilling Program (IODP) 314-316 Based on the detailed analysis of the gravitational flow sedimentation characteristics in the upper slope basin of the South China Sea Trench, the response mechanism to multi-branch faults and large earthquakes is analyzed. The results show that the South China Sea Trough accretionary wedge Up-slope basin filled with wedge-shaped body flow, gorge and surface layer flow Sedimentary: wedge-shaped body flow formed in the early stages of multi-branch faulting, showing the northern thick southern thin wedge features, reflecting the multi-branch fault The coarse-grained muddy breccia that is rich in sediments reflects the characteristics of intense activity of early multi-branch faults. The canyon system consists of dense canyons, large block flows and axial canyons, and is mainly affected by multiple branches The coupling of faults caused the steep slope, the increase of pore fluid pressure in regional formation and imbalanced uplift of the basin. The surface bulk flow was located at the top of the basin and was weak The superposition of body flow and current submarine surface is characterized by a large number of collapsed terrain with “horseshoe”, and these relatively short-term mass flow should be triggered by surface-induced earthquakes. It reflects the history of multi-branch faults and the occurrence of large earthquakes: 1.95 ~ 1.55Ma. The initial activities of multi-branch faulting are intense. The thrusting activities cause the collapsing sediments to collapse. The wedge-shaped block flow sediments at the bottom of the slope basin. 1.55 ~ 1.07Ma. Coupling of multi-branch faults to the west resulted in the east-west-low structural pattern in the slope basins and the accumulation of energy at wedges and faults in the western basin. Since 1.07Ma, energy has been intermittently released at the faults and triggered many earthquakes .