中国大陆主要地震活动区中小地震震源参数研究

本文利用中国大陆几个主要地震活动区近几年积累的大量ML≥3.0数字地震观测记录,在分别反演得到13个不同构造研究区域的介质衰减模型、348个台站的场地效应的基础上,自0.1~20 Hz的SH观测波形数据中逐步消除了仪器、噪声、几何扩散、传播路径的介质衰减、台站场地效应等影响后,恢复了2573次3.0≤ML≤6.0地震的震源谱,采用ω平方震源模型拟合震源谱后,利用Brune的圆盘模型计算了它们的震源参数,并讨论了中国大陆中小地震的震源特征,比较了中国大陆不同地区的应力降释放水平,综合讨论了地震应力降与震源深度、机制解类型、地震大小等各种因素的关系.研究表明,中国大陆中小地震释放的应力降在0.1~20 MPa之间,绝大多数在10 MPa以下.新疆天山中东段地区、青藏块体东北缘及龙门山断裂带东北缘是高应力降地震集中的区域,表明这里的断层受到相对较强的构造剪应力作用.中小地震释放的应力降随着震级的增大而增大,应力降Δσ∝M03.14,不遵循常数应力降模型.在深度20 km以内,中小地震释放的应力降对深度的依赖不显著,但在20 km以上深度显示出随深度增大而增大的现象.中小地震释放的应力降没有表现出与震源机制类型的相关性.本研究实现了震源参数的准实时计算,丰富了大陆块体内部地震震源定标率关系研究的样本.可以预见,随着中小地震数据的大量产出和积累,这些震源参数的时空分布特征研究将会为地震预测预报研究提供有实际物理意义的依据,得到的介质衰减模型及场地效应等也将对台网日常震级ML测定所需的量规函数、台站校正值的研究提供重要参考.

Study on source parameters of small to moderate earthquakes in the main seismic active regions, China mainland

On the basis of both the frequency dependent Q(f) model for 13 regions and the site response for 348 stations were inversed firstly by using different inversion methods, source displacement spectra of about 2573 events of 3.0≤M_L≤6.0 from 2001 to 2010, occurred in main seismic active regions of the mainland china, are restored after the influences of instrument, noise, geometry spreading, anelastic attenuation, as well as the site contributions were corrected from SH components of the observed seismic waves. The source parameters of 2573 events are further estimated assuming a Brune-type source model. Our results demonstrate that the estimated stress drops range from 0.1 MPa to 20 MPa with most less than 10 MPa. The stress drops of events occurred in the middle and east part of Tianshan, Xinjiang, China, the east-northern boundary of Tibet, and the east-northern segment of Longmenshan fault zone, are relatively larger, implying that they may experience relatively stronger shear stress. We find that stress drops increase with earthquake magnitudes, satisfying a relationship of Δσ∝M₀^3.14, not a constant model. We don't find a dependence of stress drop on focal depth within 20 km, while there is a minor increasing trend with depth increasing when deeper than 20 km. We don't find a dependence of stress drop on focal mechanism. Through this work, we realized the near real time calculation of source parameters for an individual event, and our results provide a large amount of samples for studying the scaling relationship in the mainland. We can prospect that with the calculation and accumulation of source parameters, the spatial and temporal characteristics of these parameters, which has certain physical meanings, will make contribution to earthquake forecasting research. In addition, the obtained attenuation model and site effects will help in determining the calibration function and station corrections, which are two important factors for the purpose of precisely estimating the local M_L magnitude.