关键词: 中国海域及邻区, 地震目录, 完整性分析, 自适应空间平滑地震活动模型, 概率增益函数

Abstract: Ocean earthquakes pose a serious threat to the security of the economic construction in coastal areas and the marine resource exploitation of China, thus the seismicity model of China’s seas and adjacent regions is one of the focuses of the next generation seismic zoning map of China. Different from mainland China, the sea area lacks multidisciplinary data such as seismic geology and geophysical exploration, thus the earthquake catalog is the most important basic data for sea area seismic activity analysis. The latest catalogue compiled by Xie et al (2020) for China’s seas and neighboring regions provides a basis for further work. The adaptively smoothed seismicity model proposed by Helmstetter et al (2007) has achieved excellent performance in the CSEP project and has become one of the most important seismicity models based on earthquake catalog. Based on the new catalog compiled by Xie et al (2020), this study for the first time established an adaptively smoothed seismicity model for China's seas and adjacent areas. Firstly, the earthquake catalogue was declustered to remove dependent events, then the completely recorded time periods were assessed for events in 0.5 magnitude intervals for every seismic zone. Furthermore, seismicity parameters such as a-value and b-value were estimated using the maximum-likelihood method provided by Weichert (1980). On this basis, the adaptively smoothed algorithm improved by Wu et al (2019) was used to build the model, and the function of probability gain per earthquake was applied to evaluate the performance of models with different parameter settings. Finally, our model was compared with the relatively traditional fixed-length smoothed seismicity model, and the advantages and limitations of our model were also discussed. Results show that: Compared with the model with a fixed smooth radius, our model has a better performance on the probability gain function, and this advantage is not affected by the minimum magnitude of the input earthquakes; When the minimum magnitude of the input earthquakes is set as M4.0, the model achieves its optimal appearance; The model’s performance not necessarily increases with smaller minimum magnitude or lager amount of input earthquakes, and a comprehensive consideration should be paid to the earthquake distribution and the catalog completeness condition of the study area when choosing parameters; Considering that this model is only based on historical and instrumental seismic catalogs and has certain limitations, it is recommended to combine our model with other models such as fault models to form a hybrid model, in order to enhance its applicability and to improve the seismicity model system. The algorithm used in this study can make full use of seismic data with varying record level over time and space, and has a certain application value in seismic hazard analysis and mid- and long-term earthquake forecast. At the same time, the adaptively smoothed seismicity model established here can be used as one of the basic models to analyze the seismic hazard for China's maritime areas, and provide technical support for the compilation of seismic zoning maps in China's sea regions. In addition, the earthquake catalog completeness analysis results and seismic activity parameters obtained in this study can provide an important reference for the seismicity analysis and the seismic hazard assessment in the sea areas of China.

Key words: China's seas and adjacent regions, Earthquake catalog, Completeness analysis, Adaptively smoothed seismicity model, The function of probability gain per earthquake