Crust–upper mantle seismic velocity structure across Southeastern China
Crust–upper mantle seismic velocity structure across Southeastern China
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DOI：
10.1016/j.tecto.2004.08.008
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发表时间：
2005-01
期刊：
影响因子：
2.9
通讯作者：
Zhongjie Zhang;J. Badal;Yinkang Li;Yun Chen;Li‐Qiang Yang;J. Teng
中科院分区：
文献类型：
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作者：
Zhongjie Zhang;J. Badal;Yinkang Li;Yun Chen;Li‐Qiang Yang;J. Teng
为了研究华夏地块与扬子地块之间的接触，1990年在中国大陆动力学项目东南段进行了一条同轴广角地震剖面。这条380公里长的剖面从安徽屯溪向西北-东南方向延伸至浙江温州。在沿记录线间隔约3公里的地震台上发射并记录了五次同轴激发。我们使用二维射线追踪模拟了P波和S波的到达，并提供了对上地壳、中地壳、下地壳、莫霍面和岩石圈地幔顶部的速度结构的约束。绘制了P波速度、S波速度和Vp/VS比值图。地壳平均厚36公里，尽管从剖面的西北端到东南端(近海)逐渐变薄。P波平均地壳速度为6.26公里/S，S波平均地壳速度为3.6公里/S。一个相对较窄的低速层，厚度约4公里，P波和S波的速度分别为6.2公里/S和3.5公里/S，标志着中地壳的底部，西北23公里，东南17公里。在壳幔转换阶段，P波和S波的速度变化较快，分别为：S(西北)7.4~7.8公里/，S(东南)8.0~8.2公里；S(西北)，S(东南)3.9~4.2公里。这一结果表明，沿该剖面约140公里采样的上地幔速度存在横向对比。平均Vp/VS值变化范围为：上地壳1.68~1.8，中地壳1.75，下地壳1.75~1.85。通过对广角地震资料的解释，认为江山-绍新断裂是扬子地块与华夏地块的分界线。
One in-line wide-angle seismic profile was conducted in 1990 in the course of the Southeastern China Continental Dynamics project aimed at the study of the contact between the Cathaysia block and the Yangtze block. This 380-km-long profile extended in NW–SE direction from Tunxi, Anhui Province, to Wenzhou, Zhejiang Province. Five in-line shots were fired and recorded at seismic stations with spacing of about 3 km along the recording line. We have used two-dimensional ray tracing to model P- and S-wave arrivals and provide constraints on the velocity structure of the upper crust, middle crust, lower crust, Moho discontinuity, and the top part of the lithospheric mantle. P-wave velocity, S-wave velocity and VP/VSratio are mapped. The crust is 36-km thick on average, albeit it gradually thins from the northwest end to the southeast end (offshore) of the profile. The average crustal velocity is 6.26 km/s for P-waves but 3.6 km/s for S-waves. A relatively narrow low-velocity layer of about 4 km of thickness, with P- and S-wave velocities of 6.2 km/s and 3.5 km/s, respectively, marks the bottom of the middle crust at a depth of 23-km northwest and 17-km southeast. At the crust–mantle transition, the P- and S-wave velocity change quickly from 7.4 to 7.8 km/s (northwest) and 8.0 to 8.2 km/s (southeast) and from 3.9 to 4.2 km/s (northwest) and 3.9 to 4.5 km/s (southeast), respectively. This result implies a lateral contrast in the upper mantle velocity along the 140 km sampled by the profile approximately. The average VP/VSratio ranges from 1.68–1.8 for the upper crust to 1.75 for the middle and 1.75–1.85 for lower crust. With the interpretation of the wide-angle seismic data, Jiangshan–Shaoxin fault is considered as the boundary between the Yangtze and the Cathaysia block.