莲花山断裂带汕尾段韧性剪切带浅层滑塌特征与成因机制

深汕特别合作区是莲花山断裂带的主要展布区，2条大型韧性剪切带从深汕区南北两侧穿过。2015年以来，区内韧性剪切带内（简称“带内”）产生了大量的浅表滑塌，发生密度远高于周边山体。因为深汕特别合作区地质灾害风险区划的需要，有必要查明带内浅层滑塌的特征与分布规律，分析其成因机制，预测其发展变化趋势。文章通过地面调查与遥感解译，查明了带内浅层滑塌的单体规模为小型，滑塌主要沿基岩面产生，滑塌体主要是土体与全风化岩体；利用信息量模型分析浅层滑塌规律，得出滑塌密度与韧性变形程度（强烈→中等→弱）、距脆性断裂的距离（近→远）、地形坡度（高→低）呈正相关，其分布密度与地貌单元、坡向、原岩类型、斜坡类型也有较强的关联。结合区域地质、勘探、气象等资料，分析得出带内浅层滑塌是在以剪切为主的多期构造作用影响形成的较弱本底条件下，在山区地块现今缓慢上升的背景下，在台风迭加暴雨的诱发下产生的，其发展变化具有迁移性、自愈性、扩展性的特点；带内斜坡在经历了2015年“彩虹”台风期间普遍性滑塌事件后，产生浅层破坏的敏感性下降，需要较长时间孕育才能进入下一次爆发期。

Characteristics and Causal Mechanism of Topsoil Slip in Ductile Shear Zone of the Shanwei Section of the Lianhuashan Fault Zone

The Shanwei Special Cooperation Zone (SSCZ) in Shenzhen is the main distribution area of the Lianhuashan Fault Zone. Two large ductile shear zones pass through the SSCZ. The ductile shear zone of the SSCZ is henceforth referred to as "the zone". Severe plastic progressive deformation, stretching, and compression occurred in the late Jurassic-Neogene period in the zone, because of which the structure and properties of the rock mass underwent significant changes. There are three levels of structural planes in the zone: brittle faults, schistosity planes, and joints in the rock mass. The ductile shearing action changes the rock mass structure, leading to poor integrity. According to existing data, the compressive strength of the rock in the zone is equivalent to 0.31-0.86 of the original rock, indicating that the strength of the rock is obviously attenuated by ductile shear action. Using ground investigation and remote sensing, we found 1,614 topsoil slips in the zone. The density of topsoil slips in the hillside area (16.2 topsoil slips per km²) was much higher than that outside the zone (1.3 topsoil slips per km²), indicating that the slopes in the zone are more prone to shallow damage. To study the geological risk zonation of geological hazards in the SSCZ, it is necessary to determine the characteristics and distribution rules of topsoil slips in the zone, analyze its causal mechanism, and predict its development trend.ⅰ) Ground surveys and remote sensing showed that monocase topsoil slip is small in the zone and sliding mainly occurs along the bedrock surface. Sliding masses are mainly solid and completely weathered rock. ⅱ) The frequency of geological disasters under the action of certain factors in the study area is divided by the frequency of geological disasters in the area. The natural logarithm of the divisor is taken as the information value to evaluate the relationship between geological disasters and various factors. The results show that the density of topsoil slips is positively correlated with the degree of ductile deformation (strong→medium→weak), distance from brittle fracture (near→far), and topographic slope (high→low). Moreover, the distribution density is strongly related to the geomorphic unit, slope direction, original rock type, and slope type. ⅲ) The above analyses are combined with regional, geological, exploration, meteorological, and other data. Results from this combination show that topsoil slips in the zone are produced under weak background conditions formed by the influence of multi-stage tectonic action dominated by ductile shear forces, the slow rise of the hillside area, and the induction of typhoons and rainstorms. Their development and changes are characterized by migration, self-healing, and expansion. ⅳ) Most of the current topsoil slips occurred during Super Typhoon Mujigae in 2015, after which the region experienced several rainfall events with intensities higher than those of Typhoon Mujigae, yet the number of topsoil slips did not increase significantly. This shows that after a general shallow sliding event, the sensitivity of the slope to shallow damage decreased, and generation took a long time before entering the next outbreak period.