晋冀蒙交界地区地震时间序列谱的分析与研究

Time series analysis and research on the earthquakes on the border of Shanxi,Hebei and Inner Mongolia

利用快速傅里叶变换和连续小波变换方法对晋冀蒙交界区1494年至2009年间发生的30个M_S≥5.0地震的时间—震级序列的准周期性进行了对比研究。研究结果显示:该区M_S≥5.0地震序列现阶段存在333年的较长稳定周期和77年的中等周期以及11年、8.6年的优势短周期,333年的长周期表明该区5级以上地震高潮期已过,但仍处于地震的较强活跃时段,77年的中等周期表明目前处于5级以上地震成组活动的低潮期,而11年的短周期显示2010年前后周期峰值达到极大值,表明2010年在77年成组活动的低潮期内有一次小的高潮,而8.6年的短周期显示周期已于2007年达到峰值极大值。相比于傅里叶变换,小波变换方法不仅能够分辨出地震活动的优势准周期性,而且能够对不同周期在不同时段的活跃程度给出清晰的描述,对当前及未来地震活动趋势的判断相对更准确。

Using fast Fourier transform and continuous wavelet transform method, the quasi-perio- dicity of time-magnitude sequences of the 30 Ms≥ 5.0 earthquakes on the border of Shanxi, Hebei and Inner Mongolia from 1940 to 2009 is comparatively analyzed. The results showed that in the Ms≥5.0 earthquake sequence in that area, there exist a longer 333-year stable cycle, a 77 years stable middle-cycle, and 11 years, 8.6 years, predominant short-cycles. The 333-year long period indicates that in the area, the peak of Ms≥5.0 earthquakes active period has expired but still in a strong active period. The 77-year cycle implies that the seismicity is in a low tide period for M〉5 earthquakes. While the ll-year period shows a short peak which achieves maximum around 2010, suggesting that there is a small high tide, occurred in 2010, in the 77-year low tide cycle. The 8.6-year short cycle shows a peak in 2007, which already achieved maximum. Compared with Fourier transform, wavelet transform method can not only identify the predominant quasi-periodicity of earthquake activity, but also be able to provide clear description of the different level of activity for different time stages and more accurate estimation of the current and future trends in seismic activity.