【摘要】 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.更多还原

【Abstract】 Nankai trough is one of seismogenic zones known for massive earthquakes in the world.Gravity flow deposits in slope basin of Nankai trough accretionary prism record the active history of magesplay faults and the recurrences of great earthquakes.Based on the data of integrated ocean drilling program(IODP),this study explores the characteristics of gravity flow deposits in slope basin and illustrates their implications to the activities of magesplay faults and great earthquakes.The results show that the slope basin was filled successively with wedge-shaped mass transport deposits(MTDs),canyon system and superficial MTDs.Wedge-shaped MTDs developed in the initial stage of magesplay fault activity,which is wedge-shaped and mainly composed of muddy breccia,indicating continuous and strong activities of the magesplay faults at the initial stage.Canyon system consists of several kinds of canyons including slope canyons,great MTDs canyon and axial canyon,which are controlled by steepening slope,increasing regional interstitial fluid pressure and anisotropic uplifting.Superficial MTDs consist of stacking multi-stage low amplitude MTDs and represent as plenty of scars,which formed in a relatively short time,but extensively.It may be caused by the seafloor shaking during agreat earthquake.These characteristics of gravity flow deposits recordthe history of magesplay fault activities and recurrences of great earthquakes as follows:1.95-1.55 Ma,magesplay fault reactivated sharply at the initial stage which triggered slumps in the upper wall of magesplay fault;1.55-1.07 Ma,coupling and activities of magesplay fault in the west domain caused strata compressed,deformed and energy assembled in the prism as well as in the magesplay fault;1.07 Ma to now,energy in the mageplay fault was released discontinuously that resulted in multi great earthquakes.更多还原