华北北部三次地震前的应变释放加速特征

强地震发生前，区域地震活动往往出现应变释放加速(AMR)现象。本文以华北地区的1976年唐山7.8级地震、1998年张北6.2级地震、2006年文安5.1级地震作为目标地震，分别分析三次主震前4~8年期间、40~120 km半径范围内的AMR现象及其特征。结果显示，唐山7.8级地震与张北6.2级地震之前均不同程度出现AMR异常，但文安5.1级地震之前并未出现。另外，本研究发现80 km半径可能是研究区寻找AMR异常有效、合理的空间扫描尺度。基于这三个震例研究的认识，本文进一步针对晋冀蒙交界地区和首都圈地区进行分析计算，结果识别出首都圈地区至目前存在AMR异常地区，这可作为判定华北北部未来强震危险性的参考。

Characteristics of Accelerating Moment Release before Three Earthquakes in Northern North China

For regional seismicity the phenomenon of accelerating moment release (AMR) usually appears preceding strong earthquakes. In this paper, taking the 1976 M_S7. 8 Tangshan earthquake, the 1998 M_S6. 2 Zhangbei earthquake and the 2006 M_S5. 1 Wen' an earthquake in the northern North China as the target events, we study the AMR phenomena and their characteristics that appeared in circular areas with radii 40 to 120 km centered at the epicenters and within the periods of 4 to 8 years before the three mainshocks. Our result shows that AMR acceleration anormalies appeared in different degrees before both the M_S7. 8 Tangshan earthquake and the M_S6. 2 Zhangbei earthquake, but did not appear before the M_S5. 1 Wen' an earthquake. Moreover, we find that the radius of 80 km would be an efficient and reasonable spatial scale for scanning and searching AMR acceleration anomalies in the study region. Based on the understanding from the three case studies, we further calculate and analyze two regions, the border region among Shanxi, Hebei and Inner Mongolia, as well as the region of the Capital circle. As a result, areas with AMR acceleration anomalies have been identified, and the result may be as a reference in analyzing and determining the future seismic risk in the northern North China.