2005-2007年四川地震的时空演化特征分析

对2005-2007年四川省内发生的262次地震(震级为3～5级)进行时间-空间分布统计分析,发现这些地震的时空演化具有一定的内在规律。通过对3年来地震数据的可视化分析,发现四川省有4个明显的地震热点地区,而且3年来这4个热点地区的地震发生频率的变化规律不一。基于球面坐标的空间分布统计分析方法,本文分析了地震的空间分布重心、地理范围,发现地震的重心具有明显的变化规律,范围不具有明显的规律性:对逐年的地震数据进分析发现,3年来地震的重心一直在向东南方向移动;将3年的数据综合为4个季度进行分析发现,第1～3季度一直向东南移动,第4季度则突然跳回到西北处;将3年的数据按12个季度进行分析,发现地震重心在前2年的8个季度中具有年周期的逆时针旋转规律,在2007年的前3个季度中,地震的重心仍逆时针旋转,第4个季度出现较大异常,重心往东南方向大跳了一步。最后以5.12汶川震中(30.986°N,103.364°E)为中心,分析了2005-2007年四川地震的空间分布的统计规律曲线,发现2007年地震出现较大的外移趋势,远离汶川地震震中。本文的研究方法和结果可以为地震的预报预测研究提供参考。

Spatiotemporal Evolution of Earthquakes in Sichuan Province Between 2005 and 2007

Using spatial statistics and data of 262 small earthquakes occurred in Sichuan province between 2005 and 2007, this paper has identified some statistical patterns in the spatiotemporal evolution of these small earthquakes.Four earthquake hotspots are obvious from the map visualization of earthquakes between 2005 and 2007,and the variations of counts of each earthquake hotspots are very different among themselves.Based on the spherical coordinate system,this paper uses a kind of spatial statistics-global spatial statistics,that is,about the center of gravity,geographical range and so on.Clear variation patterns of the center of gravity of earthquakes are identified.The center of gravity of these small earthquakes moves southeastward from 2005 to 2007; in quarterly grouping,the center of gravity moves southeastward from the first to the third quarter but shifts northwestward in the fourth quarter;the center of gravity moves counterclockwise during a period of 11 quarters,from the first quarter of 2005 to the third quarter of 2007,but shifts greatly clockwise southeast in the last quarter 2007.This paper also examines the spatiotemporal distribution of these small earthquakes with reference to their center of gravity and the epicenter of the Wenchuan Earthquake and discusses the relationship between these small earthquakes and the Wenchuan Earthquake.It is shown that,during 2007,small earthquakes are in a trend of moving outward from Wenchuan Earthquake,unlike the small earthquakes in 2005 and 2006.