腾冲火山区的地震层析成像及其构造意义  

Seismic tomography in the Tengchong volcanic area and its tectonic implication

作　　者：杨晓涛[1] 胥颐[1] 刘建华[1] 李志伟[1] 

机构地区：[1]中国科学院地质与地球物理研究所,油气资源研究重点试验室,北京100029

出　　处：《地球物理学报》2011年第8期2050-2059,共10页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40974027);中国地质调查局项目(BT-2008-04)资助

摘　　要：利用滇西南临时台网和固定台站的地震数据反演了腾冲及邻近地区的P波速度结构,着重分析了腾冲火山区和龙陵7级地震震源区的地壳结构特点.研究结果表明,腾冲火山区下方10～20 km深度范围存在明显的低速区,其横向尺度大约在20～30 km之间;推测这一低速区代表了仍处于活动状态的壳内岩浆源,热流通道有可能通过腾冲断裂延伸至地壳深部.地壳速度结构自东向西的变化显示出与不同时期的火山活动的关系,腾冲东侧偏高的速度结构反映了龙川江一带上新世时期火山通道内冷凝固结的岩浆侵入体或不易挥发的高密度残留物质。腾冲西侧的低速异常揭示了更新世以来持续至今的岩浆作用和热流活动.龙陵7级地震震源区的地壳结构存在明显的横向非均匀性.M7.3级和M7.4级地震与怒江断裂和龙陵断裂两侧的结构差异密切相关,它们分别发生在高速区和低速区的分界附近.怒江断裂东侧和龙陵断裂西侧具有较高的速度,是震源区应力积累的主要载体;两断裂之间地壳速度明显偏低,有可能是多期次的岩浆侵入导致地壳结构强度降低,使得怒江断裂和龙陵断裂易于受构造应力作用而引发强烈地震,估计地震的震源深度在10～12 km之间.Using earthquake data from a temporary network and other permanent stations in southwestern Yunnan, we inverted the P-wave velocity structure of Tengzhong and adjacent areas, with the aim to analyze the crustal structure of the Tengchong volcanoes and Longling M〉 7 earthquake areas. Our results indicate that the Tengchong volcanic area is underlain by a prominent low-velocity zone at 10-20 km depth and with a lateral extent of 20-30 km. We infer that this low-velocity zone represents an active magma source and the heat flow channel may extend into the deep crust through the Tengchong fault. The W-E variation in the crustal structure is correlated with the volcanic activities in different periods. The highTvelocity structure in eastern Tengchong reflects the cooled and solidified magma intrusions or high density remnants within the volcanic channels during Miocene-Pliocene, whereas the low-velocity zone of western Tengchong reveals the magmatic and heat flow activities from Pleistocene to present day. A strong lateral heterogeneity is observed in the crust structure of the Longling M-7 earthquake area. The occurrence of the M7.3 and M7.4 earthquakes are related to the structural variation across the Nu River fault and the Longling fault, both of which are located near velocity boundaries. The upper crust east of the Nu River fault and west of the Longling fault is characterized by high velocities, which is considered as a primary location for stress accumulation in the earthquake area; however, low velocities are observed in the region between the Nu River fault and the Longling fault. It implies that multiple magma intrusions probably decreased the rheologic strength in the crust. It is the distinct variation in the structure that made the Nu River fault and the Longling fault easy to produce seismic ruptures for the intense earthquakes under the effect of tectonic stress. We infer that these two earthquakes occurred at 10-12 km depth.

关 键 词：腾冲火山区 地震层析成像 P波速度结构 龙陵地震 

分 类 号：P315[天文地球—地震学]