Three‐dimensional elastic wave velocity structure of the western and central Tien Shan
Three‐dimensional elastic wave velocity structure of the western and central Tien Shan
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DOI：
10.1029/93jb01560
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发表时间：
1993-09
影响因子：
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通讯作者：
S. Roecker;T. M. Sabitova;L. Vinnik;Y. Burmakov;M. I. Golvanov;R. Mamatkanova;L. Munirova
中科院分区：
文献类型：
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作者：
S. Roecker;T. M. Sabitova;L. Vinnik;Y. Burmakov;M. I. Golvanov;R. Mamatkanova;L. Munirova
本文利用位于天山西部和中部的地震仪记录的近震和远震的纵波（P）和横波（S）到时，确定了该山带下地壳和上地幔的一维和三维弹性波速度结构。最佳拟合的一维结构表明，该地区莫霍罗维界面的平均深度为50公里。上地壳的三维结构显示，该区域每个主要洼地内都有厚厚的沉积物。地震活动的南倾面在深度上勾勒出楚坳陷下7 km厚的沉积楔，表明存在活动的滑脱山。这些低速连续向东南方向伊塞克湖延伸，表明两者之间存在构造关系。然而，伊塞克湖似乎并没有被消耗，而是在逆冲周围的山脉。费尔干纳盆地的低速沉积物达到10公里的深度，并在三面以无定形的地震活动带为界。中地壳深度的速度一般是低于下天山中部比下天山西部。这种模式变得更加明显，在上地幔，与P速度对比高达10%的边界，大致对应的地理位置的塔拉索-费尔干纳断层。天山中部以下的低速超过150公里的深度，但似乎不超过300公里的深度。没有证据表明在这部分山脉之下存在岩石圈根;相反，低速度意味着存在正浮力使山脉上升。有证据表明，这个低速区存在的碰撞前，天山可能不欠它的复兴，只是因为它的位置在北方边缘的一个强大的塔里木盆地，而是一个异常的上地幔，更容易变形比周围的岩石圈。
Arrival times of compressional (P) and shear (S) waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central Tien Shan are used to determine one- and three-dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt. The best fit one-dimensional structures suggest that the average depth of the Mohorovicic discontinuity in this area is 50 km. The three-dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region. A 7 km-thick wedge of sediment beneath the Chu Depression is outlined at depth by a south dipping plane of seismic activity, suggesting the presence of an active decollemont. These low velocities extend continuously to the southeast toward Issyk-Kul, suggesting a structural relationship between the two. However, rather than being consumed, it appears that Issyk-Kul is overthrusting the surrounding ranges. The low-velocity sediments in the Fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity. Velocities at midcrustal depths generally are lower beneath the central Tien Shan than beneath the western Tien Shan. This pattern becomes more evident in the uppermost mantle, with P velocity contrasts of as much as 10% across a boundary that corresponds roughly to the geographical position of the Talasso-Fergana fault. The low velocities beneath the central Tien Shan exceed 150 km depth but do not appear to be deeper than 300 km depth. There is no evidence for a lithospheric root beneath this part of the range; rather, the low velocities imply the presence of a positive buoyancy force uplifting the mountains. Evidence that this low-velocity region existed before the collision suggests that the Tien Shan may not owe its rejuvenation simply to its location at the northern edge of a strong Tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere.