THE CO2 DISCHARGES AND EARTHQUAKES IN WESTERN YUNNAN

The authors have studied the distribution of CO2 springs in western Yunnan and their isotopic composition,and suggested that there are five different sources of CO2 discharges inthat area. They are: (1) areal metamorphic origin----the Daxing CO2 spring in YunxianCounty; (2) aureloe metamorphic origin----the hot CO2 springs in the Tengchong geothermalarea; (3) remanent volcanic origin----the cold CO2 springs in the Tengchong area; (4) thermaldynamometamorphic origin----the CO2 springs in Eryuan County; (5) the mixed origin ofmetamorphic and mantle CO2----other CO2 springs distributed along the deep-great faults.Among them the mixed origin and the thermal dynamometamorphic origin CO2 discharges are related intimately to the tectonic stress change in the deep crust,therefore the capability of reflecting earthquake activity is better. We have selected the typical springs at Xiaguan and Jianggan to monitor continually the possible relations between the CO2 discharges and seismic activities. The monitoring results indicated chat,the total dissolved CO2 content in the thermal fluid showed distinctly anomalous changes before earthquakes of magnitude about 5.0 in that area,and the imminent precursor was very noticeable; and therefore monitoring the total dissolved CO2 content of the CO2 springs could be a useful method for earthquake prediction.