Analysis on Hebei Zanhuang Earthquake Swarm in 2013

YANG Rui; WANG Xiao-shan; WANG Xiang; TANG Lan-rong; LIU Li; BIAN Qing-kai; WANG Li-chan; LI Dong-sheng; CAI Ling-ling

doi:10.3969/j.issn.1003-1375.2014.04.004

Abstract：According to the records of the Hebei digital seismic network ,an earthquake swarm including 229 ML ≥ -0 .9 earthquakes occurred in Zanhuang County of Hebei Province from May 19th ,2013 to July 15th ,2013 .Historical records show that there is no earthquake of magnitude 5 occurred within 30 km .The earthquake regions of the 1966 xingtai M7 .2 strong earthquake distributed in direction of NNE ,but one NW trending branch in the south of the earthquake regions extended near the Zanhuang County ,along which ,a small quantity of ML1~2 earthquakes occurred .Compared with the relatively calm background of earthquake activity ,the Zanhuang earthquake swarm activity is very outstanding .Analysis of relationship between earthquake magnitude and frequency shows that the b‐value of the earthquake swarm is lower than the normal .On the basis of the 11 focal mechanism solutions of ML ≥2 earthquakes of the swarm inverted using the wave amplitude ratio method and seismic waveform fitting technique , the stress field in the source area is calculated which is fully consistent with the tectonic stress field of North China Region .It can be proved that the earthquake swarm was triggered by right strike‐slip faults through which the earth‐quake swarm distributed in NNE and was correspond with the nodal planes of the focal mechanism solu‐tions and most of them are NWW‐dipped .Owing to the fact that the similar focal mechanism solutions and the low b‐value both belong to the phenomenons of earthquake precursor ,the research about seismic situa‐tion tracing of Zanhuang area should be strengthened .