海原-六盘山断裂带三维精细速度结构地震环境噪声成像研究

The Haiyuan-Liupanshan fault, located at the intersection area among Tibetan Plateau, Alxa Block and Ordos Block, is an important tectonic and terrain boundary, where reveals strong tectonic activity with lots of earthquakes. Fine velocity structure of the Haiyuan-Liupanshan fault zone provides critical roles not only for exploring the contact relations between the northeast margin of the Tibetan Plateau and Ordos Block, but also for understanding the tectonic background and dynamic process of earthquake occurrence. It will develop a greater understanding of the dynamics of the northeastern margin of the Tibetan Plateau. Using the short period seismic ambient noise data recorded from a temporary seismic network, and employing ambient noise tomography, adjoint tomography methods, this project plans to investigate high-resolution 3D S-wave velocity structure of upper-middle crust in the Haiyuan-Liupanshan fault region. Meanwhile the distribution of the earthquakes in this area will be obtained using the double difference earthquake location method. Based on the velocity structure and the earthquake distribution, considering the existing results of seismic reflection profiles and magnetotelluric survey, we try to explore the geometric shape of the fault. Combining geological, geophysical and geodynamic information, we try to study the contact deformation and dynamic process between Tibetan Plateau and Ordos Block, and we also try to understand the tectonic background that causes big earthquakes.

海原-六盘山断裂带位于青藏高原与阿拉善、鄂尔多斯块体的交汇地区，是构造格局和地势分异的重要边界，构造活动强烈，地震多发。海原-六盘山断裂带区域深部精细结构的研究，是探索青藏高原东北缘与鄂尔多斯块体之间的接触变形关系的需要，也是理解地震发生的构造背景和动力过程的需要，将增进关于青藏高原东北缘动力学研究的认识。本研究拟采用地震环境噪声面波层析成像方法和伴随层析成像方法，利用分布在海原-六盘山断裂带区域的密集流动地震台阵记录的短周期连续地震环境噪声数据，反演断裂带区域中上地壳三维精细速度结构。同时，利用双差地震定位方法获得断层带区域地震分布结果。以速度结构分布为基础，结合地震定位以及已有的地震反射剖面、大地电磁剖面等资料，探讨断层深部几何形态；综合地质、地球物理、地球动力学等方面资料，研究青藏高原东北缘与鄂尔多斯块体之间的接触变形关系以及大地震孕育和发生的构造背景。

海源-六盘山断裂带位于高原东北缘与阿拉善地块和鄂尔多斯克拉通的交界处，构造复杂，地震活动强烈。获取该区域精细的地壳速度结构对于理解青藏高原东北缘及邻近地区的深部动力学环境与强震危险性具有重要意义。本研究利用研究区固定地震台网与多个流动观测台阵记录的地震环境噪声数据和地震环境噪声成像方法，结合天然地震面波，构建了地壳三维高分辨率S波速度模型。结果显示，地壳速度横向分布不均，海源弧形构造带与鄂尔多斯盆地在浅层地壳呈显著低速特征。六盘山断裂西侧的青藏高原东北缘与东侧的鄂尔多斯克拉通都存在中地壳低速层，但两者的厚度与空间分布特征有较大差异。研究区域莫霍面深度整体上青藏高原东北缘较深、鄂尔多斯较浅，同时在在六盘山地区呈现自西向东的楔入特征。研究区域地壳增厚受青藏高原东北缘的扩张直接影响，海源-六盘山断裂以西的中地壳低速层可能与地壳通道流和上下地壳运动解耦相关。