Simulation of post-seismic effects of the Maduo MS7.4 earthquake in 2021

Using the fault model issued by the USGS, and based on the dislocation theory and local crust-upper-mantle model layered by average wave velocity, the co-seismic and post-seismic deformation and gravity change caused by the 2021 Maduo MS7.4 earthquake in an elastic-viscoelastic layered half space are simulated. The simulation results indicate that: the co-seismic deformation and gravity change show that the earthquake fault is characterized by left-lateral strike-slip with normal faulting. The changes are concentrated mainly in 50km around the projection area of the fault on the surface and rapidly attenuate to both sides of the fault, with the largest deformation over 1000mm on horizontal displacement, 750mm on the vertical displacement, and 150μGal on gravity change. The horizontal displacement in the far field(beyond 150km from the fault)is generally less than 10mm, and attenuates outward slowly. The vertical displacement and gravity change patterns show a certain negative correlation with a butterfly-shaped positive and negative symmetrical four-quadrant distribution. Their attenuation rate is obviously larger than the horizontal displacement, and the value is generally less than 2mm and 1 micro-gal. The post-seismic effects emerge gradually and increase continuously with time, similar to the coseismic effects and showing an increasing trend of inheritance obviously. The post-seismic viscoelastic relaxation effects can influence a much larger area than the co-seismic effect, and the effects during the 400 years after the earthquake in the near-field area will be less than twice of the co-seismic effects, but in the far-field it is more than 3 times. The viscoelastic relaxation effects on the horizontal displacement, vertical displacement and gravity change can reach to 100mm, 130mm and 30 micro-gal, respectively. The co-seismic extremum is mainly concentrated on both sides of the fault, while the post-earthquake viscoelastic relaxation effects are 50km from the fault, the two effects do not coincide with each other. The post-seismic horizontal displacement keeps increasing or decreasing with time, while the vertical displacement and gravity changes are relatively complex, which show an inherited increase relative to the co-seismic effects in the near-field within 5 years after the earthquake, then followed by reverse-trend adjustment, while in the far-field, they are just the opposite, with reverse-trend adjustment first, and then the inherited increase. The horizontal displacement will almost be stable after 100 years, while the viscoelastic effects on the vertical displacement and gravity changes will continue to 300 years after the earthquake. Compared with the GNSS observation results, we can find that the observed and simulated results are basically consistent in vector direction and magnitude, and the consistency is better in the far-field, which may be related to the low resolution of the fault model. The simulation results in this paper can provide a theoretical basis for explaining the seismogenic process of this earthquake using GNSS and gravity data. © 2021, Editorial Office of Seismology and Geology. All right reserved.