Finite Difference Tomography of Crustal Velocity Structure Beneath Tengchong, Yunnan Province
Finite Difference Tomography of Crustal Velocity Structure Beneath Tengchong, Yunnan Province
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DOI：
10.1002/cjg2.20014
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发表时间：
2013-03
期刊：
影响因子：
--
通讯作者：
Cao Ling-min;Yi Xu;Wu Shiguo
中科院分区：
文献类型：
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作者：
Cao Ling-min;Yi Xu;Wu Shiguo
运用有限差分层析成像方法，利用临时台网和其他永久台站的地震资料反演腾冲地区地下纵波速度结构，分析腾冲火山岩浆活动和龙岭7.3/ 7.4级地震的深部构造成因。结果表明，该地区地壳速度结构具有明显的非均质性。浅层地下较低的速度是由松散的盆地沉积、新生代火山沉积、流体裂缝和温泉造成的。5 ~ 15 km深度的高速带可能代表冷却和凝固的岩浆侵入物或挥发性较低的超镁铁质残余物。地壳深部的低速构造表明岩浆处于熔融或半熔融状态。龙岭地震带火山下岩浆活动与地壳深部岩浆侵入可能来自同一岩浆底区，该岩浆底区是目前岩浆活动的主要区域。龙陵地震带具有强烈的横向非均质性。怒江断裂带东部和龙岭断裂带西部以高速为特征，岩石应变强度大，是应力积累的主要载体。两条断裂之间的低速异常向下地壳延伸，可能是地壳深部岩浆侵入所致。区内岩浆活动明显受龙陵断裂和怒江断裂控制。龙岭7.3级和7.4级地震发生在断层下方的速度边界附近。龙岭地区强震发生的主要原因包括地壳介质强度横向变化引起的应力积累的非均质性、深部岩浆聚集和动力作用。
: This work applies the finite difference tomographic method to invert P-wave velocity structure beneath the Tengchong area using earthquake data from a temporary network and other permanent stations, and analyzes the magmatic activity of Tengchong volcanoes and the deep structural genesis of the Longling M7.3/M7.4 earthquakes. The results show the velocity structure of the crust in this area has a pronounced heterogeneity. The lower velocities in the shallow subsurface are caused by unconsolidated basin deposits, Cenozoic volcanic deposits, fluid fractures and hot springs. The high-velocity zone at 5∼15 km depth probably represents cooled and solidified magmatic intrusions or less volatile ultramafic remnants. The low-velocity structure in the deep crust indicates molten or semi-molten magma. It is probable that the magmatic activity beneath volcanoes and magma intrusions in the deep crust of the Longling earthquake zone are from the same magmatic hearth area, which is the main area of the present magmatic activities. A strongly lateral heterogeneity is observed in the Longling earthquake zone. The east of the Nujiang fault belt and the west of the Longling fault belt are characterized by high velocity, implying large strain strength of rocks, which are the main carriers of stress accumulation. The low-velocity anomalies between the two faults extend to lower crust, probably caused by magmatic intrusions in the deep crust. The magmatic activity in this area is controlled clearly by the Longling fault and the Nujiang fault. The Longling M7.3 and M7.4 earthquakes occurred near the velocity boundary beneath the faults. The main reasons for the strong earthquakes in the Longling area inlcude the heterogeneity of stress accumulation caused by the lateral variation of the crustal medium strength, the deep magmatic aggregation and dynamic actions.