Seismic evidence for very deep roots of continents
Seismic evidence for very deep roots of continents
复制标题
大陆根深蒂固的地震证据
DOI：
10.1016/0012-821x(95)00215-x
复制
发表时间：
1996
影响因子：
5.3
通讯作者：
R. Kind
中科院分区：
文献类型：
--
作者：
J. Gossler;R. Kind
讨论了地震地球动力学中的一个主要问题：大陆渗透到地幔中有多深？在地球仪的大部分地区，作为SS前兆出现的地幔不连续面底面反射的差分旅行时间显示出与海洋和大陆的明显相关性。在亚洲和北美大陆下面的海底比在邻近的太平洋下面的海底大得多。从这一观察，我们得出结论，亚洲和北美大陆的影响地幔远低于410公里。过渡带厚度的变化可以解释我们的观测结果，这与岩石学相变导致410 km和660 km地震不连续的假设是一致的。大陆下面的过渡带的平均厚度比海洋下面的厚约14公里。此外，我们的研究结果意味着温度变化约100 - 200 K的地幔过渡带。只有在地球的某些地区才能观察到来自520 km深度的弱反射，对应于约2%的阻抗对比度，而来自其他位置的观测结果明确显示，该深度没有信号。因此，我们认为，520公里的反射层只是一个区域性特征。
A major problem in geodynamics with seismic data is discussed: How deeply do the continents penetrate into the mantle? Differential travel times of underside reflections from mantle discontinuities that appear as precursors to SS, in large parts of the globe, show a clear correlation with oceans and continents. They are significantly larger beneath the Asian and North American continents than underneath the neighbouring Pacific. From this observation we conclude that the Asian and North American continents affect the mantle well below 410 km. Changes in the thickness of the transition zone can explain our observations, which are in agreement with the hypothesis of petrological phase changes causing the 410 km and 660 km seismic discontinuities. Average thickness of the transition zone underneath continents is about 14 kim thicker than beneath oceans. Moreover, our findings imply temperature variations about 100–200 K in the mantle transition zone. Weak reflections from 520 km depth corresponding to an impedance contrast of about 2% can be observed only in some areas of the Earth, while observations from other locations definitively show no signal from this depth. Therefore, we propose that the 520 km reflector is only a regional feature.