2020年西藏波密ML4.9震群活动的潮汐触发特征

The Tidal Triggering Features of 2020 Bomi ML4.9 Earthquake Swarm near Eastern Himalayan Syntaxis in Tibet,China

摘要:

2020年7—8月，西藏波密发生显著震群，震群包含25次M_L≥4.0地震，最大为7月19日M_L4.9地震。震群部分相邻地震具有约24h或12h的时间间隔，这意味着波密震群地震活动可能受不同周期潮汐变化的影响。针对其中20次有震源机制结果的M_L≥4.0地震，分别计算地震前后震源机制解在2个节面上的潮汐正应力、剪应力和库仑破裂应力变化，在此基础上讨论波密震群的潮汐触发特征。结果显示，潮汐应力对波密震群地震活动有一定的触发作用，65%的震例显示潮汐应力具有明显的促滑特征，这些有触发影响的地震发生时间大多位于潮汐正应力极大值及其后的紧邻时段。研究表明，潮汐应力导致的断层张性作用增强（挤压减弱），可能是波密震群地震潮汐触发的一个主要原因。

Abstract:

A significant sieismic swarm occrrred during July to August of 2020 in Bomi region,eastern part of Tibet,which includes 25 eqrthquakes with M_L≥4.0 and the maximum of M_L4.9 that occurred on July 19. The interval between swarms is of about 24 or 12 hours,which implies that the seismic activity of the Bomi swarm may be triggered by tidal changes with differenct periods. For 20 swarms of M_L≥4.0 earthquakes with focal mechanism solutions,the tidal normal stress,tidal shear stress and tidal Coulomb fracture stress change on two nodels before and after the earthquake have been calculated respectively,and the tidal triggering features of these earthquakes have been discussed. The results illustrate that the tidal strsss has a centain triggering effect on Bomi swarm,and more than 65% cases show an obvious sliding-promoting action on earthquake initiation. The occurring time of these earthquakses are corresponding to the time periods around the maximum tidal normal strsss. This indicates that the enhanced fault tension caused by tidal stress may be one of the major causes for the tidal triggering on Bomi swarm.