地震拐角频率与地震矩对应关系研究以及自相似法则失效的机理分析

The published results and the preliminary investigation of the applicant show that the corner frequency is not always proportional to the cube root of seismic moment and breaks occur in self-similarity of earthquakes. The problems to be solved are: 1) the relation between corner frequency and seismic moment for different magnitude; 2) what is the theoretical basis for non-self-similarity of earthquakes and its effect on corner frequency and seismic source spectra; 3) how to apply the new relation between corner frequency and seismic moment to the finite source ground motion simulation method and empirical Green’s function method, in order to improve the simulated results. These problems are basic issues of seismic source physics, which is research highlight in seismology. This program will use records from earthquakes of different magnitude, the seismic source and seismic wave propagation theories, and analytical inversion methods to study these problems. The study will be helpful for obtaining the relation between corner frequency and seismic moment of large earthquakes, and understanding the theoretical basis of the break in self-similarity law of earthquakes. Meanwhile, it has important practical meaning for improving the simulation results by finite source ground motion simulation method and EGF method and improving the accuracy of seismic hazard assessment of active fault in urban area. Therefore, this program has fundamental, frontier and practical characteristics.

已有的研究结果及申请者的初步研究表明，地震震源参数不完全符合传统的相似法则，拐角频率在不同条件下不完全与地震矩的立方根成反比。现在需要解决的问题是：1) 拐角频率在不同震级时与地震矩的关系；2) 自相似法则失效的机理及其对拐角频率和震源谱模型的影响；3) 如何将新的拐进频率关系和震源谱模型引入地震动合成法，以优化该方法的地震动合成结果。上述问题涉及震源物理的基本问题，属于地震学的研究热点方向。本项目将利用不同震级的实际地震记录，运用地震震源理论以及地震波动理论等基础理论，结合波谱反演等数值分析方法对上述问题进行研究。本项目的研究对于阐释拐角频率与地震矩依赖关系的内在机理，相似法则失效的内部机理具有重要的理论意义；对于优化有限断层随机合成法和经验格林函数法的地震动合成结果，从而提高城市活动断层危险性评估精度具有重大的现实意义。因此本项目具有基础性、前沿性和实用性。

本项目针对地震拐角频率与地震矩对应关系以及自相似法则失效机理展开了研究。按照研究计划，应用震源物理、地震波动、大小地震震源定标关系及震源参数经验关系等，通过对实际地震记录（汶川地震余震记录）进行反演分析，建立了不同震级地震的拐角频率与地震矩之间的对应关系；开展了自相似法则失效的内部机理研究；将新建立的地震拐角频率与地震矩之间对应关系和优化的震源谱模型应用于地震动合成法，提高经验格林函数法的模拟精度。.实现了预期研究目标，取得了预期研究成果，主要研究进展如下：(1) 提出了一种更加精确的地震拐角频率反演方法——谱比法，避免了通过数值方法难以消除的场地效应和传播路径效应的影响，提高了地震拐角频率反演精度；(2) 推导了断层滑动速率与拐角频率的关系，通过大小地震释放能量的差异和变化，揭示了自相似法则失效的内部机理之一是大小地震断层面滑动速率的差异引起；（3）通过对汶川地震部分台站记录的数值模拟，验证了新建立拐角频率及优化的震源谱模型的有效性。