应用综合震源机制解法对辽宁及邻区现今构造应力场的初步分析

Present Tectonic Stress Field in Liaoning and Its Adjacent Areas from Composite Focal Mechanism Method

摘要:

根据辽宁测震台网最近10年记录到的6 245次天然地震，28 698个P波初动极性数据，在考虑不同震中距数据权重的同时给出辽宁及相邻地区0.25°×0.25°的精细构造应力场，并结合构造背景对反演结果进行分析。总体来看，反演得到的主压应力轴方位以NE、NEE向为主，倾伏角较小；主张应力轴方位以NW、NNW向为主，局部有近NS向分布，倾伏角近乎水平。该结果与之前学者的研究比较相近。大多数网格点的主张应力轴倾伏角小于主压应力轴倾伏角，表明辽宁及邻区处在拉张的应力状态。经分析，这与太平洋板块对亚欧板块NWW向的俯冲并导致上地幔软流圈上隆有关。此外，所得结果亦很好的呈现出在构造分区交界处局部构造应力场的相对复杂及不均匀性；综合震源机制解节面走向与研究区内主要断裂走向一致。

Abstract:

Based on 28 698 P wave polarity data of 6 245 natural earthquakes recorded by Liaoning seismic network in the last decade, we calculated the 0.25°×0.25° tectonic stress field of Liaoning and its adjacent areas by considering the weight of different epicenter distance. The inversion results in the study area were then analyzed in combination with corresponding tectonic background. In general, the inversion results indicated that the principal compressive stress axis is mainly NE and NEE, and the dip angle is small; the principal extensional stress axis is mainly NW and NNW, with local distribution of near NS, and the dip angle is almost horizontal. The results are consistent with those of previous studies. The pitch angle of principal extensional stress axis of most grid points is smaller than that of principal compressive stress axis, showing that Liaoning and its adjacent areas are in a stress state of tension. It is related to the subduction of the Eurasian plate by the Pacific plate in NWW direction and the consequent upwelling of upper mantle asthenosphere. In addition, the results also showed that local tectonic stress field at the junction of geological structure divisions is relatively complex and uneven. The nodal strike inverted by composite focal mechanism solution is consistent with the main fault orientation in the study area.