南海北部陆坡区典型峡谷陡坡群地震稳定性

Seismic Stability of Steep Slope Groups in Typical Canyons of Northern South China Sea

南海北部陆坡是一个呈条带状分布的大规模海底斜坡,西起海南岛东南部海域,向东延伸至中国台湾岛西南部海域。该区域分布了多个峡谷陡坡群,地质构造复杂、地震易发多发,滑坡地质灾害活跃。特别是该区域地形起伏较大,地震灾害可能诱发区域大面积的海底滑坡,科学评估其地震稳定性显得十分重要。本文以南海北部陆坡区神狐海域典型峡谷陡坡群为例,基于Scoops3D和GIS技术建立了三维计算模型,开展了海底陡坡群的地震稳定性研究,获得了峡谷区不同陡坡的地震稳定性安全系数及其分布特征。结果表明:峡谷剖面大多呈“U”字形,推断研究区峡谷为Ⅱ型海底峡谷系统;强震作用可以大幅削弱海底斜坡稳定性,其中对于C1峡谷区陡坡群,随着水平拟静力地震系数增大至0.40,区域最小安全系数则陡降至0.50;地震作用下西部峡谷陡坡群的失稳范围明显高于东部区域,大部分滑坡发生在两侧谷壁靠近峰顶的位置,另有相当一部分滑坡位于C1和C2峡谷区南段的东侧谷壁,整体呈带状分布。

The northern continental slope of the South China Sea is a large-scale submarine slope that extends in a belt-like configuration from the southeastern waters of Hainan Island to the southwestern waters of Taiwan Island,China.Several canyons and numerous steep slopes are located at this area.Due to the complex geological structure and earthquake-prone nature of the area,various geo-hazards such as landslides are active.In particular,due to the large topographic relief and frequently seismic activity,earthquake-induced landslides often occur in the region.So it is important to scientifically assess the seismic stability of large submarine landslides.In this study,a three-dimensional numerical model was developed using Scoops3D and GIS technology to investigate the seismic stability of typical steep slope groups located at canyons in the northern continental slope of the South China Sea.The results show that:Most of the canyon profiles in the study area are in the shape of“U”,and it is inferred that the canyons are typeⅡsubmarine canyon system.Strong seismic action can substantially weaken the stability of submarine slopes located at canyons,in which the regional minimum safety factors of steep slope groups in C1 canyon dramatically decreases to 0.50 while the horizontal seismic coefficient with the increase to 0.40.The seismic-induced destabilization range of the steep slope groups in the western canyon is significantly higher than that in the eastern region,and most of the landslides are concentrated in the valley walls on both sides near the crests of the peaks,while a considerable portion of the landslides are located at the eastern valley walls of the southern section in C1 and C2 canyons,with the overall distribution being a belt-like shape.