环渤海地区显著震群序列活动特征

Activity characteristics of significant earthquake swarms in the Bohai Rim region

为系统考察环渤海地区显著震群序列的活动特征,本文利用拟合效果较好的ETAS模型和充分考虑小震信息的OK1993模型对环渤海地区2012年以来的长岛、乳山、盖州、营海岫等显著震群序列参数进行拟合,分析震群的参数变化特征。研究结果表明:环渤海地区显著震群在时间上存在一定的差异,在空间上的差异并不显著,仅在震群发育过程中存在一定的迁徙现象;b值受震群活动影响较大,呈现多次起伏变化,在显著震群或较强地震发生前会出现不同程度的低b值现象,反应了显著地震(震群)发生前的应力累积和地震活动导致了地壳应力的调整;ETAS模型对环渤海震群序列显示了较好的拟合效果,震群的a值相对较低,级联触发程度较高,为a值作为震群判定提供了更多的震例积累;显著震群中的小震群序列活动存在一定的差异性,如长岛地区震群触发能力较强、乳山地区震群衰减相对较慢、营海岫地区震群所处应力水平较低、盖州地区震群所处应力水平较高等。上述研究对于震群序列活动特征研究以及未来震群或显著事件的预测具有重要的指示意义。

The purpose of this study is to systematically investigate the activity characteristics of the significant earthquake swarms in the Bohai Rim region.We use the epidemic-type aftershock sequence(ETAS)model with good fitting and the Ogata–Katsura 1993 model with full consideration of small earthquake information to fit the sequence parameters of the significant earthquake swarms since 2012,including Changdao,Rushan,Gaizhou,and Yinghaixiu,and analyze their parameter variation characteristics.The results show that the significant earthquake swarms have some differences in time but not in space,and only some migration phenomena exist in their development processes.The b value is significantly affected by the activity of earthquake swarms,with many fluctuations.Before the occurrence of significant earthquake swarms or strong earthquakes,there are different degrees of low b phenomenon,reflecting the stress accumulation before significant earthquakes(earthquake swarms),and the activity of earthquake swarms leads to the adjustment of crustal stress.The ETAS model shows a good fitting effect on the sequence of the Bohai Rim earthquake swarms.Theαvalue of the earthquake swarms is low,and the cascade triggering ability is high,which also produces more earthquake events for the determination of theαvalue as an earthquake swarm.There are some differences in the activity of small earthquake swarms among the significant earthquake swarms;for example,the triggering ability of the Changdao earthquake swarm is stronger,the attenuation of the Rushan earthquake swarm is slow,the stress level of the YinghaiXiu area is lower,and the stress level of the Gaizhou area is higher.This study is of great significance to the investigation of the activity characteristics of earthquake swarm sequences and the occurrence of future earthquake swarms or significant events.