汶川地震频次场异常特征分析

地震频次场是描述地震发生频次时空特征的一种数学方法。将2008年5月12日汶川8.0级地震震中附近区域（30.0°~33.0° N、101.5°~105.5° E）作为研究对象，以自然正交函数展开方法分析频次场典型场时间因子的时间变化特征。当取前8个特征值对应的典型场时，拟合精度可达0.936 8；其中6个典型场显示有异常变化，占总场比重的0.691 1；异常出现时间最早在2004年9月，即震前3年7个月，最迟在震前1个多月，表现出短临异常特征。研究结果表明利用地震频次场方法能够较为理想地提取汶川8.0级地震震前异常。

Characteristics of frequency field anomalies beforethe Wenchuan earthquake in 2018

The earthquake frequency field is a mathematical method to describe the temporal and spatial characteristics of seismic frequency. Taking the area near the epicenter of Wenchuan M_S8.0 earthquake on May 12, 2008 (30.0°-33.0°N, 101.5°-105.5°E) as the research area, the time variation characteristics of typical field time factors of frequency field were analyzed with the expansion method of natural orthogonal function. When the typical fields corresponding to the first eight eigenvalues were taken, the fitting accuracy reached 0.936 8, and six typical fields showed abnormal changes, accounting for 0.691 1 of the total field. The anomaly occurred in September 2004 at the earliest, that is, 3 years and 7 months before the main shock, and more than 1 month before the main shock at the latest, showing the characteristics of short-term and imminent anomaly. The results showed that the seismic frequency field method can ideally extract the anomalies before the Wenchuan M_S8.0 earthquake.