基于混合方法的南海海域地震动衰减关系研究

Derivation of ground motion attenuation relation for earthquake in the South China Sea areas based on a hybrid method

我国南海海域面临俯冲带地震的影响,海域俯冲带地震的工程特性是海域工程抗震研究的基础,为给海域工程地震危险性分析提供合理的地震动输入,对于没有实际地震动数据的我国南海海域,文中提出一种基于数值模拟结合其他区域已有经验衰减关系建立本地衰减关系的方法。该方法采用随机有限断层法分别对南海俯冲带和日本东北部俯冲带板内地震动进行模拟,以模拟的不同震级、不同距离下的大量地震动为基础,回归了日本俯冲带与南海俯冲带地震动衰减关系,并推导二者的定量关系,基于此定量关系和已知的日本东北部俯冲带板内地震的经验衰减关系,最终建立南海俯冲带板内地震动的衰减关系。将文中建立的南海地震衰减关系与日本以及汶川地震衰减关系进行对比,结果表明:不同类型的地震的衰减特征存在一定的差异性,海域俯冲带板内地震的衰减速率要快于我国陆地地区的汶川地震的浅地壳地震;数值模拟结合经验关系的混合方法得到的南海俯冲带板内地震动衰减关系具有一定的应用价值,此方法可为没有实际地震动的地区建立衰减关系提供参考,建立的衰减关系可为海洋工程和近海交通重大工程的建设提供依据。

The South China Sea is located close to the subduction zone, and the engineering characteristics of subduction zone earthquakes is the basis of sea area seismic research. In order to supply reasonable ground motions for hazard analysis of offshore engineering, for the South China Sea without actual seismic data available, a method of establishing the local attenuation relationship was proposed based on the numerical simulations and the empirical attenuation relationships from other regions. In this method, the stochastic finite fault method was employed to simulate the ground motions of intraplate earthquakes for subduction zones of the South China Sea and the northeastern Japan. Based on these simulated ground motions of different magnitudes and epicentral distances, the ground motion attenuation relationships for these subduction zones were regressed. Hence, the quantitative relationship of the two subduction zones were obtained, and based on the quantitative relationship and the empirical attenuation relationship of Japan subduction zone, the earthquake attenuation relationship of intraplate earthquakes for the subduction zones of the South China Sea was eventually established. By comparing the attenuation relationship proposed in this work with those for Japan and Wenchuan earthquake, it is found that： the attenuation characteristics of different earthquakes have regional differences; the ground motion attenuation rate of the intraplate earthquakes for the subduction zones of sea is faster than that of the shallow crustal case such as the Wenchuan earthquake; the attenuation relationship for intraplate earthquake of the subduction zones established by the hybrid method of numerical simulation and empirical attenuation relationship, shall be applicable and can be referred by those regions without actual ground motions. Therefore, theestablished earthquake attenuation relationships can be referred by marine and offshore engineerings.