华北地区强震活动状态研究

华北地区历史强震活动频繁, 但自1998年张北6.2级地震后至今6级以上地震平静近22年。 大家对该区域未来6级以上地震危险趋势非常关注, 且有不同观点。 本文分析了该区6级以上地震活跃—平静周期性, 运用小波变换技术对周期成分进行了定量计算; 对比研究了活跃期与平静期之间的过渡阶段(本文称其为过渡幕)地震活动特点及其持续时间; 从1999—2018年地震应变释放率与第Ⅲ、 第Ⅳ活跃期、 第3平静期和第Ⅳ活跃期内第3、 第4平静幕的对比、 平静幕持续时间的统计特征、 当前华北地区显著的5级地震平静以及该区6级和7级以上地震前5级以上地震活动状态等方面进行了研究。 结果显示, 支持当前华北地区进入平静期的依据相对较多。

Active State and Trend on Strong Earthquakes in North China

Historic strong earthquakes occurred frequently in North China, while the earthquakes with M_S≥6.0 has been quiet for nearly 22 years since the 1998 Zhangbei M_S6.2 earthquake. Scholars are very concerned about the activity trend of strong earthquakes and there are different views. This paper discusses the rhythmic characteristics of active and quiet periods of earthquakes with M_S≥6.0, applies the technique of Morlet wavelet transform to quantitatively analyze the seismicity periodicities, and compares the seismicity features and duration time of the transition section from the active to quiescent period. It is studied that the spatial distribution of earthquakes in active periods, the comparison of strain release rates in active period, quiet period and quiet episode, statistical characteristics of the quiet episode duration time, the currently remarkable seismic quiescence of M_S≥5.0 earthquakes, and regional seismicity features of M_S≥5.0 earthquakes before the earthquakes with M_S6.0~6.9 and with M_S≥7.0 in North China. It is believed that the present situation is in the transition section or has been entered the quiet period.