腾冲火山地震群的活动特征

CHARACTERISTICS OF EARTHQUAKE CLUSTER ACTIVITY IN TENGCHONG VOLCANIC AREA

根据 1998 ,1999和 2 0 0 2年腾冲火山区流动数字地震台网的 3期观测资料 ,从中选择出 30个与岩浆活动有关的地震事件 ,这些事件主要以地震群的形式出现。从地震群的时空强分布特征、各观测台的地震波记录特征、震源参数和震源机制等方面 ,分析研究区内火山地震群的活动与岩浆囊体位置的关系。结果表明 ,腾冲火山区存在 2个岩浆囊体 ,一个位于北纬 2 5 0°～ 2 5 1° ,东经 98 4 2°～98 4 8° ,深度约 4～ 6km ;另一个位于北纬 2 4 9°～ 2 5 0 5° ,东经 98 4 5°～ 98 5 5°,深度约 8～ 14km以下。地震群活动主要围绕在岩浆囊体的周围 ,与岩浆活动密切相关。

Thirty seismic events related to magmatic activities have been selected from observation data of the mobile digital seismic network disposed in Tengchong volcanic area in 1998, 1999 and 2002. These selected events mainly occurred in cluster. The relations between the activities of volcanic earthquake clusters and the locations of magma chambers are analyzed on the basis of space-time-magnitude distributions of earthquake clusters, seismic wave characteristics, focal parameters and focal mechanisms. The anomalies of S wave records of specific event show that there are magma bodies or magma channels beneath the southern Tengchong volcanic area; focal mechanisms display that the orientation of earthquake-generating stress corresponds well with that of the regional tectonic stress. Seismic fractures are dominated mainly by horizontal strike-slip, but some seismic fractures display relatively large dip-slip components. It is inferred that the volcanic earthquake clusters are the results of shear-fracturing of the wall rocks in the vicinity of the magma chamber caused by the activities of heat medium under the action of regional tectonic stress. This study shows there are two magma bodies beneath Tengchong volcanic area: one is located at 25 0°～25 1°N, 98 42°～98 48°E and 4～6km depth, the other is located at 24 9°～25 05°N, 98 45°～98 55°E and 8～14km depth. The activities of earthquakes are mainly around the magma bodies and greatly related to magmatic activities. Magma bodies control the geothermal activity and micro-fracturing in Tengchong volcanic area.