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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1) 江晓涛1) 吴朋2) 杨宜海1)
1)成都理工大学,成都市成华区二仙桥东三路1 号610059;2)四川省地震局,成都市人民南路三段29 号610041
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. 8 km / 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. 4 km / 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,并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:国家自然科学基金重点项目(40839909)和国家自然科学基金项目(41074062)资助
Research on crustal flow and dynamic characteristics in Sichuan and its adjacent area
Fan Jun1,2) Zhu Jieshou1) Jiang Xiaotao1) Wu Peng2) Yang Yihai1)
1) Chengdu University of Technology,Chengdu 610059,China;2) Earthquake Administration of Sichuan Province,Chengdu 610041,China
Abstract:
On the basis of the broadband data of regional seismic stations from the Sichuan Seismic Network and the mobile seismic stations,the receiver function inversion method was adopted for studying the characteristics of crustal flow and dynamic effects in Sichuan and its adjacent area. The results showed that the crust and upper mantle velocity in the Sichuan basin is significantly higher than the eastern edge of the Qinghai-Tibetan plateau. The earth’s crust velocity vS is from 3. 6 to 3. 8km / s,and the upper mantle velocity vS is from 4. 0 to 4. 5km / s. And there is no low-velocity layer in the crust. The lithology showed a nature of strong block. In the eastern edge of Qinghai-Tibetan plateau,the velocity vS is in low speed,the average velocity vs in earth’s crust is from 3. 0 to 3. 4km / s,and the upper mantle velocity vS from 4. 0 to 4. 5km / s. Low-velocity layer appear frequently in the crust. Most of the low-velocity layers are located in the intermediate crust with the depth of 20km to 40km. A small number of low-velocity layers appear in the upper crust of 10km ~ 20km and lower crust of 40km ~ 60km. Affected by the Indian Plate northward,the eastern margin of the Qinghai-Tibetan plateau moved in the eastward direction. It was blocked in hard Sichuan Basin. The movement is in the southeastward and southward direction. The movement process is produced by the complicated force in the research area. Because of this,the eastern margin of the Qinghai-Tibetan plateau become complicated geological structure and intense seismic activity area. Low speed crustal flow by strong Sichuan Basin barrier is delaminated into two or three shunts upward and downward. The shunts into upper crust uplift the surface,forming steep peaks. The downward flow intrudes into lower crust and the upper mantle. It makes the crust thickened and Moho sinking. Crust flow is mainly distributed along the active faults of the eastern margin of the Qinghai-Tibetan plateau. In the eastern margin,mainstream flow is from central Qiangtang block,and along the NW-SE direction along the Xianshuihe fault,then turned south and has two branches: a southward branch along the Anninghe fault and Xianshuihe fault,the other along the Nujiang River fault,Lancangjiang River fault zone to the south. In the research area in the north,there is a NE and EW crustal flow to the Longmenshan Mountain fault.
Key words:  Sichuan and its adjacent area  Receiver function  Crust flow  Dynamic characteristics