南海北缘钻探选址:滨海断裂带大型海洋地质灾害研究

Oceanic drilling into the northern margin of the South China Sea:investigating the great marine geohazards along the Littoral Fault Zone

滨海断裂带是南海北缘的一条大型活动断裂带,其位置靠近我国华南沿海地区。滨海断裂带全长超过1200 km,包括西段(北部湾-阳江),中段(珠江口)和东段(粤东-福建)。其西段和东段历史上至少曾发生过4次大地震(M7+),中段目前是一个大地震空区。在经济高速发展和人口高度密集的今天,如果滨海断裂带再次发生大地震并触发海啸,必将对我国华南沿海地区造成灾难性破坏。由于缺乏完整的历史地震记录和针对古地震的钻孔沉积研究,目前尚不清楚滨海断裂带大地震的准确次数、空间分布和复发周期,以及中段大地震空区的主要原因(断层蠕滑或大地震周期较长),因此无法有效评估该断裂带的大地震破裂分段和灾害风险。本研究总结了滨海断裂带的构造特征、重点描述了3次历史大地震及引发的灾害影响,和国际上针对海底大地震的钻探研究经验。根据这些信息,本文建议在断裂带的西段、中断和东段进行大洋钻探,获取穿过断层带的关键沉积和岩石样品,利用沉积古地震方法重建滨海断裂带东段和西段的大地震历史和复发周期,研究断层带的岩石物理性质,揭示滨海断裂中段大地震空区的成因,解析断层分段式破裂的原因,为我国海洋防灾减灾提供重要的科学依据。

The Littoral Fault Zone is a major active fault zone in the northern margin of the South China Sea,close to the coastal region of the southern China.The Littoral Fault Zone is more than 1200 km long,consisting of the west segment(Beibu Bay-Yangjiang),the middle segment(Pearl River Mouth),and the east segment(Yuedong-Fujian).At least 4 large earthquakes(magnitude>7)have occurred inthe west and east segments,while its middle segment was exempt.As the economy is rapidly growing and the present day population density is high,the littoral fault will cause enormous destruction to the coastal area of southern China if it generates great earthquakes and the ensuing tsunamis in future.Due to lack of complete historical earthquake records and oceanic drilling study on the paleoseismicity,there is lack of clarity on the precise quantity,spatial distribution and recurrence period of great earthquakes along the Littoral Fault Zone,and the nature of great earthquake quiet zone(aseismic slip or longer recurrence period of great earthquakes),which in turn leads to poor understanding of earthquake mechanism and associated risk of marine geohazards.This study summarizes the structural characteristics,describes the hazard influences of 3 large earthquakes along the Littoral Fault Zone,and introduces the international oceanic drilling studies on great earthquakes.Based on this information,we propose to carry out oceanic drilling into the west,middle and east segment of the Littoral Fault Zone,recover essential sediments and rocks through the fault zone,reconstruct the history and recurrence period of paleoseismicity along west and east parts of the Littoral Fault Zone,study the physical properties of fault zone rocks to identify the cause of earthquake quiet zone in the middle part of the Littoral Fault Zone,analyze the mechanism behavior of fault segments,finally providing critical scientific basis for the marine hazard preparedness and mitigation strategies.