关键词: 印尼8级地震, 云南水位异常, 机理

Abstract: Two large earthquakes occurred continuously in the sea northwest of Sumatra,Indonesia,on 26 Dec.2004 and 29 Mar.2005.The observation of water level in Yunnan recorded abundant information about the two earthquakes.This paper presents the water level response to the two earthquakes in Yunnan and makes a preliminary analysis.The present digital water level recording may possibly lose some information,so large earthquake caused abnormal change of water level recorded by analog recording is clearer than that by digital recording.The well water level rise or decline caused by the two large earthquakes respectively was centralized in a small tectonic unit divided by large faults in Yunnan,and the change of water level rise or decline is evidently correlated with geological configuration.Water level rise or decline may be correlated with the change of regional stress field,but it wasn't caused by the change in direction of original stress field.The recent tectonic stress field in Yunnan is mainly divided into three areas.The first area is located east of Xiaojiang Fault;the second located in Sichuan-Yunnan Rhomboid Block,west of Xiaojiang Fault,north of Honghe Fault and east of Jinshanjiang fault;and the third located west of Honghe Fault.Water level rise or decline areas caused by Indonesia large earthquakes are not consistent with subareas according to direction of original stress field.The direction of stress field west of Lancangjiang Fault is basically same,but the change of water level caused by Indonesia large earthquake is divided into two sections by Nandinghe Fault,the north rises and the south declines.We think the reason for water level rise or decline is possibly that the seismic wave changes the stress state of the tectonic unit.Abnormal change of water level caused by large earthquake is mainly attributed to well water bearing bed responding to seismic wave.The change is mainly elastic deformation,so the records are mostly water wave-like as seismic wave.Because of difference of hydrogeologic conditions and effect of regional stress field and seismic wave additive stress field,the water bearing bed appeared to be in a stress adjustment stage after earthquake in a block or a fault.So in some wells,changes of water level rise or decline appeared,and the changes are also correlated with geological configuration.The two Indonesia large earthquakes occurred along the Sumatra Fault,its focal mechanism is similar to reverse fault.The shape of recordings of water level response to the two earthquakes in a same well is very similar except amplitude.So we inferred the water level response mode in same well is completely same for earthquake occurring on same fault and its fracture mode is similar,the difference is just that the response amplitude increases with the growth of magnitude.

Key words: Indonesia large earthquake, abnormal water level in Yunnan, mechanism discussion