Moho depth, seismicity and seismogenic structure in China mainland
Moho depth, seismicity and seismogenic structure in China mainland
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中国大陆莫霍面深度、地震活动及发震构造
DOI：
10.1016/j.tecto.2013.11.008
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发表时间：
2014-07
期刊：
影响因子：
2.9
通讯作者：
Yongqian Zhang
中科院分区：
文献类型：
--
作者：
Jiwen Teng;Yangfan Deng;José Badal;Yongqian Zhang
1958年以来，基于中国大陆广角地震剖面的地壳-上地幔结构研究为岩石圈的构造和变形提供了更严格的约束；但是，地震速度结构与地壳发震层之间的联系仍然是一个悬而未决的问题，我们对此特别感兴趣。从沿着许多地震剖面获得的地壳p波速度模型开始，我们绘制了东亚下的莫霍深度图。在大陆边缘和海域，莫霍深度在20 ~ 28 km之间。中国大陆发生的地震大多在4级以下。平均焦深与莫霍深之比约为0.3。将自然地震活动性的下界作为位于震源90%以上的深度，我们分别在上述区块的21、41、30和36 km处发现了这一极限。在中国北部和东北部，一些地震发生在莫霍线以下（平均深度41公里对38公里），尽管这里观测到的平均震源深度只有12公里。一旦将发震层定义为集中了80%释放的地震能量的层，我们就会发现，相对于其他两个上下延伸的地壳层，东亚的地震速度差在0.1到0.9 km/s之间。这一发现有助于区分产生地震能量的能力较大或较小的地方。地震速度差大于0。
The study of the crust–upper mantle structure based on wide-angle seismic profiles performed in China mainland since 1958, has provided tighter constraints on the architecture and deformation of the lithosphere; but the link between the seismic velocity structure and the seismogenic layer of the crust is still an open problem in which we are particularly interested. Starting from the crustal P-wave velocity models obtained along numerous seismic profiles, we have mapped the Moho depth beneath East Asia. The results demonstrate that the average Moho depth is about 35 km in Southeast China, 38 km in North and Northeast China, 51 km in Northwest China and 65 km in Tibet. The Moho depth varies between 20 and 28 km in the continental margin and sea area. Most of the earthquakes in China mainland have magnitude lower than 4.0 and generally occur in the uppermost 20 km of the crust and therefore above the Moho discontinuity; the average focal depth is found at 10 km in Southeast China, 12 km in North and Northeast China, 15 km in Northwest China and 13 km in the Tibetan Plateau. The ratio of the average focal depth to the Moho depth is approximately 0.3. Taking the lower bound of the natural seismicity as the depth above which is located 90% of the foci of earthquakes, we have found this limit at depths of 21, 41, 30 and 36 km in each of the mentioned blocks, respectively. In North and Northeast China some earthquakes occur below the Moho (at 41 km depth on average versus 38 km), although the average focal depth observed here is of only 12 km. Once defined the seismogenic layer as the layer that concentrates 80% of the released seismic energy, we have found that the difference in seismic velocity with respect to the other two crustal layers which extend above and below varies from 0.1 to 0.9 km/s in East Asia. This finding enables to discriminate the place with greater or lesser capacity to generate seismic energy. A difference in seismic velocity bigger than 0.9 km/s would mean that the layer has an earthquake generating capacity lesser than the seismogenic layer, as greatly happens in South China and Northwest China; while a smaller velocity difference would imply that the layer has a comparable seismogenic capacity, as happens in Tibet.
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