琼北东寨港桥头村大桥沉没于海时间考与1605年琼州大震后东寨港缓慢下沉速率及机理  

A study on the time of bridge sinking into the sea at Qiaotou village in Dongzhai port,northern Hainan Province and slow sinking rate and mechanism of Dongzhai port after Qiongzhou earthquake

作　　者：徐起浩[1] XU Qihao(Seismological Bureau of Guangdong Province,Guangzhou 510070,China)

机构地区：[1]广东省地震局,广东广州510070

出　　处：《古地理学报》2024年第3期725-752,共28页Journal of Palaeogeography：Chinese Edition

摘　　要：琼北东寨港桥头村大桥和大桥前面条石路面废墟,现今位于退潮后水面下并被淤泥覆盖,仅小部分出露。据家谱、墓碑考证和实地调查,该大桥在1605年琼州大震后45年、即公元1650年尚在使用,是琼州大震后,又经近百年才沉没于海的。1650年后至今(截至调查年1984年),东寨港桥头村地区地面以不低于1.5 cm/a的速率下沉;近30~40年来东寨港中段和北段以不低于1 cm/a速率缓慢下沉,南端下沉速率小些。琼州大地震后的早期,东寨港的下沉速率可能更大些。本研究粗略估算了这次地震同震下沉幅度东寨港中部和北部可能达2~3 m。南部下沉幅度小些。对震后缓慢下沉机理进行了讨论,认为琼州大震是在新生代以来至震前各地质时期,琼北地幔柱隆起、地壳隆起拉张破裂、火山多次活动或喷发、地壳减薄表部下沉、壳下持续性强烈活动的背景下发生的。震前琼北特别是琼北东部地壳经历了数千年的隆起,积聚巨大能量形成壳下热点。震前因地下水向拉张断裂的贯入,降低断裂面摩擦力,震前陆地开始下沉,并终于全面突破断裂面摩擦阻力发生陆陷成海大地震。震时释放部分能量,震后剩余能量对断裂持续拉张,东寨港持续地堑型沉陷。地震时及震后相当长时间内海水对断裂快速和持续贯入降低了断裂面上的摩擦力,使震后断裂呈相对稳定滑动,这些可能是震后东寨港数百年来大速率缓慢下沉的主要原因。连接琼州大地震,晚更新世及可能迟至全新世早期以来,东寨港经历过由陆变海、由海变陆、又由陆变海的演变过程。The ruins of the Qiaotou village bridge and the strip stone pavement in front of the bridge in Dongzhai port,Northern Hainan Province,are now submerged under the water surface at low tide and covered with mud,with only a small portion exposed.According to genealogical records,tombstone inscriptions,and field investigations,the bridge was still operational 45 years after the Qiongzhou earthquake,specifically in 1650 AD.It indicates that the bridge sank into the sea nearly a century after the 1605 Qiongzhou earthquake.The research shows that since 1650,the ground in Qiaotou village area of Dongzhai port has been subsiding at a rate of no less than 1.5 cm per year according to recent survey in 1984.The survey also shows that in the past 30~40 years,the ground of central and north section of Dongzhai port have slowly subsided at a rate of not less than 1 cm/a.The sinking rate was likely higher in the early period following the Qiongzhou earthquake.This paper roughly estimates that the amplitude of coseismic subsidence of this earthquake may reach about 2~3 m.The paper discusses the mechanisms behind slow subsidence after the earthquake,attributing it to persistent intense activity beneath the crust due to mantle plume uplifts,crustal stretching,and fracturing,accompanied by multiple volcanic activities or eruptions over various geological periods since the Cenozoic.Prior to the earthquake,the crust of northeastern Hainan,had been uplifting for thousands of years,accumulating significant energy and forming sub-crustal hotspots.The reduction in friction on the fault surfaces due to groundwater penetration into the tension fractures initiated the land subsidence,culminating in a significant earthquake that caused extensive land to sink into the sea.After earthquake,the residual energy continuous to stretch the fault,resulting in continuous graben type settlement of crust in Dongzhai port.The rapid and continuous penetration of seawater into the fault during and after the earthquake reduced the friction force on the frac

关 键 词：琼北 地震事件 震后下沉速率 断裂拉张 海水沿断裂贯入 稳定滑动 

分 类 号：P546[天文地球—构造地质学]