青藏高原Moho界面起伏样式对通道流模型的动力学响应——基于数值模拟

Geodynamic response of Moho relief modes to the channel flow below the Tibetan Plateau:numerical simulation

青藏高原的高精度人工源深部地震探测发现:壳一幔边界(Moho)并非是一物理学上的"刚性"界面,它不仅起伏变化强烈,极为凹凸不平,而且被一系列规模不一,产状各异的深大断裂所切割,故必然会导致复杂的地表和深部物质运移动力学响应的复杂化.在常见的通道流模型中,一般均设定下地壳与上地幔之间为一平缓界面,在数值模拟工作中亦常简化为平滑的约束界面.为此,基于青藏高原实际资料提取的壳、幔介质平均速度模型,采用黏弹性数值模型讨论Moho界面起伏变换样式对通道流模型产生的响应.研究结果表明:(1)通道流效应的影响仅限于小区域内,当Moho面存在起伏样式变化时,确会对通道流产生影响,Moho界面的起伏增强了下地壳和岩石圈地幔的同步运动效应,但是其影响范围是有限的;(2)Moho界面起伏形态变化对地表和Moho界面水平位移产生的影响各异,在Moho界面发生错断的地方,呈现为地表水平位移开始发生明显加速减小的地方,即地表与深部介质水平位移解耦,模型深部动力学效应与地表的响应并非为局部性效应,而至少体现出区域性的响应.

The crust-mantle boundary（Moho）is not a ＇rigid＇ interface in physics as evidenced by high-precision artificial source deep seismic sounding in the Tibetan Plateau.This interface is not only extremely uneven with large relief,but also cut by a series of deep faults with different sizes and different geometries.Therefore,it should have complex dynamic responses of material motion on the surface and in the deep subsurface.In the common channel flow model,the interface between the lower crust and upper mantle is assumed as a flat boundary,and simplified into a smooth constrained boundary in numerical simulation.This paper adopts 2-D viscoelastic models to simulate the response of the channel flow model by an undulating Moho interface.These models are based on the average velocities of the crust and upper mantle of the Tibetan plateau extracted observational data.The results shows that the effect of channel flow is limited to a small area.The changes of Moho relief can affect the channel flow.The undulating Moho interface enhances the synchronous motion of the lower crust and lithospheric mantle,but in a limited range.The changes of Moho shape produces different influences on horizontal displacements on the surface and the Moho interface.Where the Moho occurs dislocation,the horizontal displacement on the surface begins to significantly reduce,implying decoupling of displacement between the surface and subsurface.The deep dynamic effects of the model and the response of the surface are not of local characters,instead at least regional processes.