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四川及邻区地壳流与动力特征研究
范军1,2) 朱介寿2) 江晓涛3) 吴朋1) 杨宜海2)
1) 四川省地震局,成都市人民南路三段29号,成都 610041 ;2) 成都理工大学,成都市成华区二仙桥东三路1号,成都 610059 ;3)中国电建集团贵阳勘测设计研究院有限公司,贵阳 550081
摘要:
利用四川地震台网区域地震台站和布设于该地区的流动地震台站的宽频带地震资料,采用接收函数反演等方法,对四川及邻区地壳流动与动力作用特征进行研究。结果表明,四川盆地地壳及上地幔速度显著高于青藏高原东缘。盆地中地壳vS值达3.6~3.8km/s,上地幔vS值为4.5~4.8km/s,且地壳内无低速层, 岩性上显示为刚强的地块。青藏高原东缘各台站的vS 断面最显著的特征是速度值很小,中地壳vS平均值为3.0~3.4km/s,上地幔vS 值为4.0~4.5km/s。地壳内普遍存在低速层,大部份低速层位于深度20~40km的中地壳,在深度为10~20km的上地壳及40~60km的下地壳中,也出现少量的低速层。受印度板块向北推移的影响,青藏高原东缘在向东运动的过程中受到坚硬的四川盆地的阻挡,产生向南及南东运动。这些运动过程的产生是由于研究区受到较为复杂的力的作用。正是在这些力的作用下,青藏高原东缘成为地质构造复杂、地震活动强烈的地区。低速的地壳流受到刚强的四川盆地的阻挡出现拆层现象,它拆分为向上及向下的2或3支分流。向上的分流侵入上地壳引起地表隆升,形成陡峭的高峰。向下的分流侵入下地壳以至上地幔,使地壳加厚莫霍界面下沉。青藏高原东缘地壳流主要沿活动断裂带上分布。它从青藏高原东缘中部羌塘地块流出,主流沿北西南东的鲜水河断裂带流动,然后转向南北沿安宁河及小江断裂向南。在研究区域的北部,还有1支北东向及东西向到龙门山的地壳流。
关键词:  四川及邻区  接收函数  地壳流  动力特征
DOI:
分类号:
基金项目:
Research on Crustal Flow and Its Dynamic Characteristics in Sichuan and Its Adjacent Area
Fan Jun1,2),Zhu Jieshou2), Jiang Xiaotao3),Wu Peng1) and Yang Yihai2)
1) Earthquake Administration of Sichuan Province,Chengdu 610041,China/2) Chengdu University of Technology,Chengdu 610059,China/3) Power China Guiyang Engineering Corporation Limited,Guiyang 550081,China
Abstract:
Using the broadband seismic data of the regional stations in the Sichuan Digital Seismic Network and the mobile seismic stations in this region,the receiver function inversion method was adopted to study the characteristics of crustal flow and dynamic effects in Sichuan and adjacent areas. The results show that: Velocity in the crust and upper mantle of the Sichuan basin is significantly higher than that beneath the eastern margin of the Qinghai-Tibetan plateau. The velocity vS is from 3. 6 to 3. 8km/s in the crust and 4. 5 -4. 8km/s in the upper mantle beneath the basin,and there is no low-velocity layer in the crust. The lithology shows a hard block. The vS velocity in the eastern margin of the Qinghai-Tibetan plateau is lower,with average vS of 3. 0 - 3. 4km/s in the mid crust and 4. 0 - 4. 5km/s in the upper mantle. Low-velocity layers are distributed widely in the crust,most of which are in the mid crust at a depth of 20km -40km,and there are also a few low-velocity layers appearing in the upper crust at depths of 10km - 20km and the lower crust at depths of 40km - 60km. Affected by the northward pushing of the Indian plate,the eastward movement of the eastern margin of the Qinghai-Tibetan plateau is blocked by the hard Sichuan basin,producing a southward and southeastward component. Such movement process is produced by the complicated forces acting in this area. Just under the action of these forces,the eastern margin of the Qinghai-Tibetan plateau becomes a region with complicated geology and intensive earthquake activity. Obstructed by the hard Sichuan basin,the low-velocity crustal flow is delaminated and split into two or three upward and downward tributaries. The upward flow intruded into the upper crust,causing uplift of the earths urface,forming mountain crests; the downward flow intruded into the lower crust and upper mantle,resulting in thickening of the crust and depression of the Moho. The crustal flow in the eastern margin of the Qinghai-Tibetan plateau is mainly distributed along the active faults. The crustal flow flows out from the Qiangtang block in the middle part of the eastern margin of the Qinghai-Tibetan plateau, the mainstream flows along the NW-SE trending Xianshuihe fault zone,then turns NS and flows to the south along the Anninghe and Xiaojiang faults. There is another crustal flow in the north of the study area,flowing in the NE and E-W directions to the Longmenshan faults.
Key words:  Sichuan and its adjacent area  Receiver function  Crustal flow  Dynamic characteristics