广东省强地震震源区地壳速度结构及其对板内地震成因的启示

Crustal Seismic Velocity Structure in the Epicenters of Strong Earthquakes in Guangdong Province and Their Implications for the Causes of Intraplate Earthquakes

稳定板块内部的强地震(震级大于和等于6.0级的地震)是如何孕育与发生的一直以来是悬而未决的科学问题。广东省的阳江洋边湾、河源新丰江水库与汕头南澳岛位于稳定的华南陆块内部,是广东省地震活动最为活跃的三个区域,有强震发生的历史,是理解板内强震孕育与发生的理想窗口。而这些强震区域的地壳结构与物理性质是理解强震孕育构造背景与发生机制的关键基础。本文基于阳江与河源已构建的上地壳速度结构,结合区域地震活动性分析,对比与总结汕头南澳岛与北美新马德里强震区的孕震构造背景,揭示广东省强震震源区与地震活跃区的地壳结构与物理性质、强震孕震与发震构造背景以及两者关系,进而探讨广东省强震发生的成因机制。结果显示广东省的强震倾向于发生于NE-SW向与NW-SE向断层交汇处。这些断层交汇处呈现低地震波速度特征,在发震深度范围(8~15 km深)地震b值较小(<1.0)。低地震波速度与低地震b值特征指示断层交汇处为稳定华南陆块的局部薄弱带,易于构造应变能积累。此外,流体参与的孔隙压力增大或荷载增大等局部地壳应力扰动可能是触发广东省强震一个不可忽略的因素。本文提出进一步加强板内强震发生的应力积累方式和持续时间,以及孔隙水压力增大的物理机制等研究,可加深认识板内强震的发生过程及其控制因素,助力粤港澳地区的地震危险性评估。

How strong earthquakes(earthquakes with a magnitude greater than or equal to 6.0)within the interior of stable plates can be conceived has always been an unresolved scientific question.The Yangbian Bay in the Yangjiang area,the Xinfengjiang Reservoir in the Heyuan area,and Nan’ao Island in the Shantou area in Guangdong province are situated within the stable South China Block.They are the most seismically active areas in Guangdong province,with multiple historically strong earthquakes.These regions are therefore the best places to explore the causes of intraplate earthquakes.The crustal structure and physical properties of the seismogenic regions of these strong earthquakes are fundamental to understanding the tectonic background and causes of such strong earthquakes.Based on the constructed upper crustal velocity structures of the Yangjiang and Heyuan areas,combined with regional seismicity analysis,this paper compared the seismic tectonic background of Nan’ao Island,Shantou,Guangdong province,and the New Madrid Seismic Zone of North America,and revealed the linkage among the crustal structure,physical properties,and seismogenic tectonic background of strong intraplate earthquakes.We further provided new insights into the causes of strong intraplate earthquakes in Guangdong province.The results showed that strong earthquakes in Guangdong province tend to occur at the fault intersection points.The fault intersection is commonly a local weak zone within the stable and rigid blocks.These weak zones are usually characterized by low earthquake b values and are prone to tectonic stress accumulation.Additionally,local crustal stress disturbances,such as pore pressure elevation or increased loads,could be essential in triggering large intraplate earthquakes in Guangdong province.Further detailed studies on the mechanisms of stress accumulation,duration of strong intraplate earthquakes,and physical mechanisms of pore pressure elevation could deepen our understanding of the occurrence processes of strong intraplate earthquakes and relevant controlling factors.This study provides a solid basis for seismic hazard assessment in the Guangdong-Hong Kong-Macao-Greater Bay Area,China.