滇西地区地壳浅部基底速度细结构的研究

The Investigation of Fine Velocity Structure of the Basement Layer of Earth' s Crust in Western Yunnan Region

本文论述滇西地区思茅—中甸剖面基底层速度细结构的研究结果。 基底层项部P_g界面深度为0—3.5km,而底部P°_1界面深度为11.0—17.0km。基底层速度在金河—洱海断裂以南为5.70—6.30km/s,断裂以北增至6.30—6.50km/s,其过渡带位于剑川附近。剖面上断裂附近,除界面深度变化外,P_g面速度横向变化也较明显。 速度等值线较为稀疏的景云桥炮南侧、大仓炮附近与支梯炮南侧地区,估计发生了岩浆沿大断裂上涌,在基底层内形成较大的侵入岩带。在景谷地区,估计玄武岩在基底层下部形成穹状结构,造成普洱—思茅一带强地震活动区,剑川一带可能情况也类似。断裂活动的挤压作用还造成基底层内等速度线的紧密分布及其倾角变化,而断裂破碎带的影响导致此处速度偏小,大断裂又往往造成基底层上下界面的某种程度同步变化,并在P_g面上形成凹陷,这些地区的地震活动比别处相对活跃。

In this paper the results of investigation of fine velocity structure in the basement layer of Simao - Zhongdian DSS profile in Western Yunnan region are discussed.The depth of upper Pg interfase of the basement layer is about 0-3. 5km,and the depth of lower P10 interface-11. 0 to 17. 0km. The velocity of basement layer in southern part of Jinhe -Erhai deep fault is 5. 70 - 6. 30km/s, and it has increased to 6. 30-6. 50km/s in northern part of it. This transition zone is situated near Jianchuan county. At the region of profile where crossed over the faults the lateral variations of Pg interface velocity are quite distinct besides the depth variation of it.The velocity isolines arranged relatively sparse near the southern region of JYQ S. P. near the DC S. P. and the southern region of ZT S. P. Maybe the magma have risen up along deep faults to the upper crust in these places, and it formed a large intrusion zone in the basement layer. At the region of Jinggu county the basalt magma maybe formed a vaulted structure in the lower part of basement, it caused the more intensive activity of seismicity nesr the Simao and Pu' er region of Yunnan Province, and it also maybe took place near the Jianchuan region. The pressing act of fault activity also caused denser arrangement of velocity isolines and variance of its dip angle in the layer,and fracture zones of faults resulted to that the velocity here became more less. Deep faults often led to that the upper and lower interfaces of basement layer had a some depth variance in the same places,and some deppressed areas on the Pg interface is often formed here. In these areas the seismicity are more active than others. All these results are clearly shown in this profile