中国海域及邻区统一地震目录及其完整性分析

UNIFIED EARTHQUAKE CATALOG FOR CHINA’S SEAS AND ADJACENT REGIONS AND ITS COMPLETENESS ANALYSIS

地震目录是开展活动构造、地震区划、地震预测和防震减灾等工作的重要基础,对地震目录的完整性、可靠性进行分析是地震学研究的基本前提之一。目前,中国海域及邻区统一的地震目录编纂及其完整性分析尚属空白。基于此现状,文中广泛收集了中国海域及邻区的地震台网、全球地震台网的分布情况和地震资料,并基于此开展了以下工作:1)研究了不同海域、不同时段的地震观测能力;2)分析了中国海域及邻区地震震中定位精度的时、空分布特点;3)采用正交回归方法拟合了中国海域及邻区面波震级、体波震级与矩震级之间的转换关系式,建立了中国大陆地震台网与中国台湾地区地震台网ML震级、中国大陆地震台网与菲律宾地震台网MS震级的转换关系式,并最终建立了中国海域及邻区统一震级标度的地震目录;4)基于震级累积频度(N-T)关系分析了中国海域及邻区统一地震目录不同范围、不同震源深度各震级档的完整起始年限。本研究是中国国内首次针对海域地震活动特征进行的海域及邻区统一地震目录的编制工作,填补了中国海域及邻区地震目录编制的空白,为中国海域及邻区活动构造、地震活动性和地震危险性分析提供了基础,为编制海域地震区划图以及海域建设规划和工程建设的防震减灾工作提供技术支撑。此外,文中对地震监测能力的分析可为今后地震台网的优化布局提供科学参考。

China’s seas and adjacent regions are affected by interactions among the Eurasian plate,the western Pacific plate,and the Philippine Sea plate.Both intraplate and plate-edge earthquakes have occurred in these regions and the seismic activities are frequent.The coastal areas of China are economically developed and densely populated.With the development and utilization of marine energy and resources along with the development of national economy,the types and quantity of construction projects in the marine and coastal areas have increased,once an earthquake happens,it will cause huge damage and loss to these areas,therefore,the earthquake-related research for these sea areas cannot be ignored and the need for study on these areas is increasingly urgent.One type of essential basic data for marine seismic research is a complete,unified earthquake catalog,which is an important database for seismotectonics,seismic zoning,earthquake prediction,earthquake prevention,and disaster reduction.Completeness and reliability analysis of an earthquake catalog is one of the fundamental research topics in seismology.At present,four editions of earthquake catalogs have been officially published in China,as well as the earthquake catalogue compiled in the national fifth-generation earthquake parameter zoning map,these catalogs are based on historical data,seismic survey investigations,and various instrumental observations.However,these catalogs have earlier data deadlines and contain the earthquake records for only the offshore regions of China,which are extensions of coastal land.Distant sea regions,subduction zones,and adjacent sea regions have not been included in these catalogs.Secondly,there were no cross-border areas involved in the compilation of earthquake catalogs in the past.It was not required to use magnitudes measured by other countries’seismic networks and observation agencies to develop an earthquake catalog with a uniform magnitude scale,moreover,there was no formula suitable for the conversion of magnitude scale in China’s seas areas and adjacent regions.Little research has been conducted to compile and analyze the completeness of a unified earthquake catalog for China’s seas and adjacent regions.Therefore,in this study,we compiled earthquake data from the seismic networks of China and other countries for China’s seas and adjacent regions.The earthquake-monitoring capabilities of different sea areas at different time periods were evaluated,and the temporal and spatial distribution characteristics of epicentral location accuracy for China’s seas and adjacent regions were analyzed.We used the orthogonal regression method to obtain conversion relationships between the surface wave magnitude,body wave magnitude,and moment magnitude for China’s seas and adjacent regions,and established magnitude conversion formulae between the China Seismic Network and the ML magnitude of the Taiwan Seismic Network and the MS magnitude of the Philippine Seismic Network.Finally,we developed an earthquake catalog with uniform magnitude scales for China’s seas and adjacent regions.On the basis of the frequency-magnitude distribution obtained from the magnitude-cumulative frequency relationship(N-T)and the Gutenberg-Richter(GR)law,we conducted a completeness analysis of the unified earthquake catalog for China’s seas and adjacent regions,Then,we identified the beginning years of each magnitude interval at different focal depth ranges and different seismic zones in the earthquake catalog.This study marks the first time that a unified earthquake catalog has been compiled for China’s seas and adjacent regions,based on the characteristics of seismicity in the surrounding sea regions,which fills the gap in the compilation of the earthquake catalogue of China’s seas and adjacent areas.The resulting earthquake catalog provides a basis for seismotectonics,seismicity study,and seismic hazard analysis for China’s seas and adjacent regions.The catalog also provides technical support for the preparation of seismic zoning maps as well as for earthquake prevention and disaster reduction in project planning and engineering construction in the sea regions.In addition,by evaluating the earthquake-monitoring capability of the seismic networks in China’s seas and adjacent regions and analyzing the completeness of the compiled unified earthquake catalog,this study provides a scientific reference to improve the earthquake-monitoring capability and optimizing the distribution of the seismic networks in these regions.