| 鄂尔多斯地块西缘莫霍面起伏及泊松比分布 |
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| 引用本文： | 许英才,王琼,曾宪伟,马禾青,许文俊,金涛.鄂尔多斯地块西缘莫霍面起伏及泊松比分布[J].地震学报,2018,40(5):563-581. |
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| 作者姓名： | 许英才 王琼 曾宪伟 马禾青 许文俊 金涛 |
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| 作者单位： | 1.中国合肥 230026 中国科学技术大学地球和空间科学学院 |
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| 摘 要： | 收集了鄂尔多斯地块西缘的21个宁夏区域地震台网台站和183个中国地震科学探测台阵台站记录到的2015年1月至2016年1月期间的远震P波资料，通过对其进行反褶积提取接收函数，并利用H-Kappa叠加方法计算了研究区内的莫霍面深度和泊松比。结果表明:研究区的莫霍面深度在36—58 km范围内变化，大体呈南厚北薄、西厚东薄的特点，且具有明显的分区特征，即以香山—天景山断裂为界，莫霍面在南北向呈现明显的起伏变化，该断裂以南的地壳增厚方式可能与青藏高原的水平挤压力所导致的上地壳重叠有关；贺兰山东麓断裂两侧的莫霍面深度落差明显，这可能是由于青藏高原东北缘NE向的挤压力以及阿拉善地块与鄂尔多斯地块之间NW?SE向的拉张力共同作用所致。研究区的泊松比整体较高，其中鄂尔多斯地块的平均泊松比要高于青藏高原东北缘的平均泊松比，银川地堑内的高泊松比现象可能与黄河—灵武断裂为超壳断裂有关；研究区内的莫霍面深度与地表高程具有较好的正相关性，说明其地壳均衡效应较好，而整个研究区内泊松比与莫霍面深度的线性关系并不明显。此外，本研究还进一步揭示了研究区内莫霍面深度与泊松比反相关最明显的两个区域，这种明显的反相关关系也表明，构造上的挤压力或拉张力更容易集中在长英质的弱岩层而使地壳增厚或减薄。综上进一步认为，从海原断裂至香山—天景山断裂这一区域及贺兰山东麓断裂两侧区域下方的地壳成分以长英质岩石为主。
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| 关 键 词： | 鄂尔多斯地块西缘 接收函数 H-Kappa叠加 莫霍面深度 泊松比 构造应力 |
| 收稿时间： | 2017-12-25 |
Moho depth and Poisson’s ratio distribution in the western edge of Ordos block |
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| Institution: | 1.School of Earth and Space Sciences，University of Science and Technology of China，Hefei 230026，China2.Institute of Earthquake Forecasting，China Earthquake Administration，Beijing 100036，China3.Earthquake Agency of Ningxia Hui Autonomous Region，Yinchuan 750001，China |
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| Abstract: | This paper collects P-waveforms of teleseismic events occurred from January 2015 to January 2016 recorded by 21 Ningxia regional seismic network stations and 183 China-Array seismic stations deployed in western edge of Ordos block, and extracts receiver functions by deconvolution, and then calculates the Moho depth and Poisson’s ratio in the studied area by using H-Kappa stacking method. The results show that the Moho depth ranges 36?58 km, which is presented as thick in the south and west and thin in the north and the east, exhibiting obvious subarea characteristics. Bounded by the Xiangshan-Tianjingshan fault, the Moho depth has a distinct change in the north-south direction, and to the south of the fault the crust-thicken way is probably related to upper crust overlap due to the horizontal extrusion from Tibetan Plateau. On the both sides of Helanshan eastern piedmont fault, the Moho depth varies largely, which may be caused by the joint impact from the extrusion in NE direction from northeastern Tibetan Plateau and the tension in NW-SE direction between Alxa block and Ordos block. In the studied area, the Poisson’s ratios are relatively high in general, and the average of the Poisson’s ratio of Ordos block is higher than that in northeastern Tibetan Plateau. On the other hand, high Poisson’s ratio in Yinchuan graben is possibly related to Huanghe-Lingwu fault as an ultracrustal one. The Moho depth is positively correlated to the surface elevation, suggesting that the crust is in the better state of isostasy, but there is no obvious linear correlation between Poisson’s ratio and Moho depth in the whole studied area. However, further study finds that there are two distinct areas, in which Poisson’s ratio is inversely correlated with the Moho depth, illustrating that the tectonic extrusion or tension is easier to concentrate on the felsic incompetent beds, which leads to the crust thickening or thinning. Consequently, from the inverse relationship between the Poisson’s ratio and Moho depth, it is believed that the crustal composition consists chiefly of felsic rocks beneath the zone from Haiyuan fault to Xiangshan-Tianjingshan fault and on the both sides of Helanshan eastern piedmont fault. |
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