Two great earthquakes occurred in the sea northwest of Sumatra,Indonesia,on December 26,2004 and March 29,2005.The observation of water levels in Yunnan yielded abundant information about the two earthquakes.This paper presents the water level response to the two earthquakes in Yunnan and makes a preliminary analysis.It is observed that the large earthquake-induced abnormal water level change could be better recorded by analog recording than by digital recording.The large earthquake-caused water level rise or decline may be attributed to the effect of seismic waves that change the stress in tectonic units,and is correlated with the geological structure where the well is located.The water level response mode in a well is totally the same for earthquakes occurring on the same fault and with the same fracture mode.The only difference is that the response amplitude increases with the growth of the earthquake magnitude.
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