海南岛东寨港1605年地震陷落事件的地球化学证据

GEOCHEMICAL EVIDENCES OF THE LAND SUBSIDENCE INDUCED BY THE HISTORICAL EARTHQUAKE IN 1605,HAINAN ISLAND,CHINA

1605年海南岛东寨港发生了重要的地震陷落事件,本文在东寨港采集了305cm长的柱状岩芯DX孔,对岩芯进行了粒度、年代学、地球化学元素的分析,发现地球化学元素在164cm附近有明显的突变,岩芯沉积物岩性特征与地球化学元素均反映了从陆相沉积向海相沉积的转变,对海南岛东寨港地震陷落事件有明显的沉积响应,岩芯沉积记录反映1605年东寨港地震沉陷的幅度至少2.0m。

The Dongzhai Bay,located in the north-eastern part of the Hainan Island.The serious earthquake in the year of 1605 occurred at Qiongzhou（present Haikou City）in the region close to present Dongzhai Bay,which was the most extensive earthquake recorded in the historical documents in South China with the seismic magnitude of 7.5 and the intensity of 10 degrees.This historical earthquake resulted in the land subsidence and the formation of the Dongzhai Bay.According to the Ming Dynasty ＂Qiongzhou Government Document＂,a strong earthquake occurred on July 131605A.D.The ground sounds came from northeast like depressing thunder with vibrating and the local governmental halls,private houses mostly collapsed in Qiongzhou.In the town of Qiongzhou,the death number was about thousands people.In the coastal region large areas of land,villages sunk in to the sea.So the Dongzhai Bay is a very young bay related to the historical earthquake in the year of 1605.In the past decades,the Qiongzhou Earthquake in the year of 1605 was interested by the Chinese researchers. The serious earthquake in the year of 1605 occurred at Qiongshan was the most extensive earthquake recoded in the historical documents in South China with the seismic intensity of M7.5.It is an interesting research to study the sedimentary records of the earthquake subsidence in Dongzhai Bay,Hainan Island.Based on the analysis of the core samples,sedimentary characteristics and elements composition changes,the coastal sedimentary respond to the historical earthquake was presented and the analysis indicated the at least 2.0meters subsidence influenced by the earthquake in the western part of the Dongzhai Bay.The 305cm long DX Core at Daoxue Village（19°55.876＇N, 110°35.806＇E） was collected and sampling with the intervals of 2.5cm,sedimentary characteristics,grain seize and elements composition changes are obviously related to the earthquake.The coastal sedimentary respond to the historical earthquake was presented in this paper.In the column of the DX Core,the marine sediments covered the red soil strata,and the red soil layer was the terrestrial environment before the earthquake subsidence.Rapid changes of the geochemical elements occurred at 164cm of DX Core and which indicated the paleo-environment shifted from terrestrial to marine environment quickly.