全球地震震源深度统计分析与地震层分布

地震数据可以反演地球内部的构造信息，能够查明地球内部层圈结构及地震发生的机制，对揭示地球结构，进行地震预测及防震减灾具有重要意义。与此同时，对地震数据的统计分析可以获得地壳变形及其深度层次的相关信息。本文利用美国地质调查局（USGS）记录的1900～2018年近3 000 000条全球地震数据进行分析，立足地震震源计算方法，排除不确定性数据，使用震源深度频次分析及高斯分解得到地震层和地震集中区深度的推定。以国际地震中心（ISC）的1970～2016年近2 000 000条数据及中国国家地震科学数据共享中心2009～2018年近300 000条数据进行比较。结果显示，地球标准椭球体深度10 km左右普遍存在一个全球性的地震集中区，与地壳中脆韧性过渡带一致。其上的地壳是全球绝大多数地震发震的深度范围，推定其为地震层；与此同时，局限在洋壳俯冲带中，约35 km处出现了另一个地震集中区，认为是地球岩石圈深度内不容忽视的界面。研究表明，在地球表层（40 km以内），层圈结构对地震有较大的控制作用；而对有洋壳俯冲区域的地震三维结构图成图显示有“贝尼奥夫带”形态，表明俯冲机制能将具有弹性力学性质的刚性块体带至地球较深部，并孕育中、深源地震。因此，地震震源分布可以指示地震层，即刚性块体，在岩石圈中的分布，地震震源深度集中区是岩石圈和中、上地幔最主要的变形和能量释放区。

Statistical analysis of global earthquake focal depth and distribution of seismic layer

Seismic data can help us to explore earth??s inner layer structure and the physical mechanisms of earthquake, providing meaningful knowledge on evaluation and prevention of earthquakes. Furthermore, the statistical analysis of seismic data can be informed of the relevant information of crustal deformation and its depth levels. The purpose of this study was to analyze over 3 000 000 global seismic data from 1900 to 2018 recorded by the United States Geological Survey（USGS）, assuming that the seismic layers and the depth of concentrating area of earthquakes by applying frequency analysis and Gaussian multi-peaks fitting method. It was compared with nearly 2 000 000 data from 1970 to 2016 by the International Seismological Centre（ISC）and nearly 300 000 data from 2009 to 2018 by China Earthquake Data Center. The results revealed that there was a global seismic concentration area at the depth of 10 km under the ellipsoid earth surface, and the depth is consistent with brittle-ductile transition zone in the crust. The majority of earthquakes were originated within these 10 km of crust. This particular layer, in span of 10 km from earth surface, were thereby presumed as the seismic layer. In the oceanic subduction zones, another seismic concentration zone was observed at the depth of 35 km below the surface, highlighting its significant role in the lithosphere. In the shallow layers of the earth（within 40 km below the surface）, the layer structures were observed to play a significantly greater role in the earthquake generation. The 3-D seismic structure map of the oceanic crust subduction area showed the “Benioff zone” shape, indicating that the subduction mechanism might pull those rigid blocks with elastic mechanics properties to deeper layer of the earth, thereby breeding earthquakes of intermediate to deep foci. Accordingly, the distribution of earthquake foci revealed the distribution of earthquake layers which are rigid blocks in the lithosphere; in addition, the concentration area of earthquake focal depth would be the main deformation and energy release zone of the lithosphere and the middle and upper mantle.