Probing into the mechanism of earthquake swarms:a case study of the 2022 Barkam earthquake swarm
Earthquakes are among the most devastating natural disasters that affect humanity.Understanding the mechanism behind earthquake initiation and propagation holds crucial scientific and societal significance for seismic hazard mitigations.In contrast to foreshock-mainshock-aftershock and mainshock-aftershock seismic patterns,earthquake swarms are prone to causing more extensive damage.Hence,an in-depth investigation into the mechanisms governing earthquake swarm genesis is imperative.On June 10,2022,a swarm sequence of earthquakes,including three moderate to large earthquakes with magnitudes of Ms5.8,Ms6.0,and Ms5.2,occurred in Barkam,Aba Prefecture,Sichuan Province,whose accurate relocation results and reliable source parameters provide a good data base for such research.In this paper,a viscoelastic model is established based on the kinematic parameters of faults,and the possible seismogenic mechanisms of the Barkam swarm are discussed from the perspectives of energy accumulation and release on seismogenic faults according to the theories of elastic dislocation and pore fluid diffusion.The results of stress loading simulations on the seismogenic fault system indicate that it is possible for parallel faults to be stressed evenly and simultaneously during the same interseismic period,which will lead to a swarm of events of similar magnitude.Considering the possible stress-triggering effect between the events in a swarm,this paper also calculated the coseismic Coulomb stress changes in the Barkam earthquake swarm sequence,and found that the events were not triggered by coseismic static stress transfers.Moreover,our simulation suggests that the effective friction coefficient of the seismogenic fault of the Barkam swarm was decreased by the fluid activity before the earthquake,which contributed to the rupture of the fault,and the pore pressure change caused by the fluid adjustment after the earthquake further promoted the occurrence of subsequent earthquakes.
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