中国大陆7级以上地震频次场时空异常特征

本文以地震频次作为地震活动的变量，通过自然正交函数展开方法，计算中国大陆7级以上强震前的地震活动频次场，提取出强震前时间因子和空间等值线的异常。结果表明，强震前时间因子出现超过均方差的高值或低值异常，异常多数分布在频次场的前4个典型场，具有多分量特点，第1个典型场异常贡献率最大(占总场40%～60%),绝大部分强震前5～8年出现长期异常，部分强震前1～2年出现中期异常，少数强震前3月出现短临异常的特征。区域频次等值线出现的高梯度旋涡区域是异常危险区，等值线值大于0.9且具有活动构造的危险区往往是强震的发震位置。另外，地震频次场与传统方法的区域地震活动频次(3月)震例对比，表明频次场时间因子异常具有自己的独特优越性和缺陷，并讨论了这些方法的差异性。

Spatio-temporal Anomalies of the Seismic Frequency Field above M7 Earthquakes in Chinese Mainland

In the paper, seismic frequency are taken as the indications of the seismicity before strong earthquakes above M7, which are calculated by means of the natural orthogonal function expansion method, and the abnormal change of time and space factor are extracted before the strong earthquakes. Results show that, before the strong earthquake, the time factor has a high or low value anomalies exceeding mean square error, most abnormal distributes in the first four typical frequency fields, showing the characteristics of multi-components. Amorry of them, the first typical field anomalies is most contribution (generally 40%~60%). Before strong earthquakes, mose cases have long-term anomalies in 5~8 years, some cases have medium-term anomalies in 1~2 years, and a few cases have short-term or imminent anomalies. The area with high gradient vortex in frequency contours in the abnormal region, in which the area with isoline value greater than 0.9 and overlaping with activce tectonics indicates the possible position for future mainshock. In addition, the comparison between the frequency field and the 3 months frequency by the traditional seismic method shows that the time factor anomaly of the frequency field has its own unique advantages and disadvantages, the differences of these methods have been discussed.