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河北省数字地震台网在2013年5月19日至7月15日记录到河北赞皇县发生震群活动,ML-0.9级以上地震229次。震群附近30km之内之前没有发生过5级以上地震,1966年邢台7.2级地震区呈北北东向分布,在其南部存在北西向分支,抵达赞皇附近,发生过少量ML1~2级小震。与较为平静的地震活动背景相比,赞皇震群尤为突出。通过分析震级—频度关系,震群呈现低b值特征;利用振幅比法反演震群ML2级以上11个基本一致的震源机制解,并进一步反演震源区应力场,结果与华北构造应力场完全吻合。结果显示,震群呈北北东方向分布,震源机制也有相应的节面对应,大多数倾向北西西,表明震群为右旋走向滑动。同时,低b值和震源机制一致属于震兆现象,应注意加强赞皇附近区域的震情跟踪研究。
Hebei Digital Seismograph Network recorded earthquake swarm activities in Zanhuang County, Hebei Province, from May 19 to July 15, 2013, with 229 ML-0.9 earthquakes. No earthquakes of magnitude 5 or above occurred within 30km near the earthquake swarm. In 1966, the 7.2 magnitude earthquake area of Xingtai was northeastward and northerly distributed in the south of it. It reached the vicinity of Zanhuang, and a few ML1-2 small shock. Compared with the relatively calm earthquake background, Zanhuang earthquake swarm is particularly prominent. By analyzing the relationship between magnitude and frequency, the swarm shows a low b-value. By using the amplitude ratio method, 11 basic consistent focal mechanism solutions over ML2 are retrieved and the stress field in the source region is further inverted. Field exactly match. The results show that the earthquake swarms are distributed in the NE direction, and the focal mechanisms correspond to the corresponding nodal planes, most of them are in the northwestern direction, indicating that the swarm swings to the right-lateral strike. In the meantime, the low b-value and focal mechanism are all consistent with the earthquake truncation phenomenon, so we should pay attention to strengthening the earthquake tracking in the vicinity of Zanhuang.