Relationship between chemical element changes in ground water and medium & strong earthquakes

Researching the abnormal changes characteristic of ground water elements and the seismic activities in Sichuan and nearby regions, we find that within 1～2 years before an Ms5 5 earthquake, the chemical element changes in ground water are able to be measured and in the area of intensive observing stations, two items in the chemical element changes in ground water and the short impending abnormal changes are able to be measured before a medium or strong earthquake one year Abnormal changes goes well with seismic events But the distribution of the observing stations which may result in a wrong conclusion should be carefully studied