A seismic refraction experiment in the Tyrrhenian Sea
A seismic refraction experiment in the Tyrrhenian Sea
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第勒尼安海地震折射实验
DOI：
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发表时间：
1986
期刊：
影响因子：
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通讯作者：
K. Louden
中科院分区：
文献类型：
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作者：
Jeremy D. Duschenes;M. Sinha;K. Louden
摘要我们提出了两个100公里长的反向地震折射线拍摄的第勒尼安海，使用爆炸源和海底接收器的结果。通过横向变化的结构使用射线追踪的结果进行了解释。更东面的T2线拍摄于第勒尼安深海平原的中部，水深3.5公里。这里的地壳显示出海洋的性质，但表现出显着的横向不均匀性。地壳的上部（第2层）包含一个陡峭的速度梯度，在典型的2公里深度处，从大约4到超过6公里s-l。地壳下部（第3层）的速度梯度较小，在地壳底部为6.6至6.9 km s-l。地壳总厚度在6至8公里之间。另一条线，T1，在科尔纳利亚盆地2.7公里的水中进行，揭示了一个更复杂的速度结构。我们的结论是，它的南半部是由海洋地壳，类似于在T2观察到的。然而，它的北方似乎是由地壳的厚度相似，但其中地震速度增加缓慢，从4.9公里s-l以下的表层沉积物在莫霍面6.3公里s-l的深度。我们将后一种结构解释为大陆地壳变薄。令人惊讶的是，海底地形和莫霍面深度都没有反映出从大洋地壳到大陆地壳的过渡。我们从这些结果中推断，虽然第勒尼安盆地的南部和东部主要是由海底扩张形成的，但大约40“N以北的盆地大部分地区，可能包括水深超过3 km的一些地区，都是由薄大陆地壳覆盖的。因此，第勒尼安盆地北方部分的演化必然主要是通过大陆伸展过程发生的，在某些地区，大陆伸展使地壳厚度减少到6-8公里。北纬40度以南。
Summary. We present the results of two 100 km long reversed seismic refraction lines shot in the Tyrrhenian Sea, using explosive sources and oceanbottom receivers. The results have been interpreted using ray-tracing through laterally varying structures. The more easterly line, T2, was shot in the central part of the Tyrrhenian abyssal plain, in a water depth of 3.5 km. The crust here is shown to be oceanic in character, but to exhibit significant lateral heterogeneity. The upper part of the crust (layer 2) contains a steep velocity gradient from about 4 to over 6 km s-l at a depth of typically 2 km. The lower part of the crust (layer 3) contains a smaller velocity gradient, from 6.6 to 6.9 km s-l at the base of the crust. Total crustal thickness is between 6 and 8 km. The other line, T1, carried out in the Cornaglia Basin in 2.7 km of water, reveals a more complicated velocity structure. We conclude that its southern half is underlain by oceanic crust, similar to that observed at T2. However, its northern half appears to be underlain by crust of similar thickness, but in which seismic velocities increase slowly with depth from 4.9 km s-l immediately below the superficial sediments to 6.3 km s-l at the Moho. We interpret this latter structure as thinned continental crust. Surprisingly neither the seafloor topography nor the depth to Moho reflect the transition from oceanic to continental crust. We infer from these results that although the southern and eastern parts of the Tyrrhenian basin were formed primarily by seafloor spreading, much of the basin north of about 40"N and probably including some areas with water depths in excess of 3 km, is underlain by thinned continental crust. The evolution of the northern part of the Tyrrhenian basin must therefore have occurred chiefly through a process of continental extension, which in some areas has reduced crustal thickness to as little as 6-8 km. South of 40"N.