Postseismic poroelastic rebound based on groundwater level observations：Taking the 2000 Iceland earthquakes as an example

Postseismic poroelastic rebound is a phenomenon that the crustal deformation continues after an earthquake due to the diffusion of pore pressure changes caused by the earthquake. Previous studies indicate that the long-term （up to 200 days following the main shock） surface deformation is well described by afterslip and viscoelastic relaxation. However, for the short-term deformation, afterslip tends to be biased by neglecting the poroelastic rebound in the upper crust. In this study, we investigate the deformation characteristics of postseismic poroelastic rebound effects taking the two Iceland earthquakes in 2000 as an example. We use numerical simulation methods to calculate the pressure changes caused by the earthquakes and the time series of groundwater level responses, and then use the coseismic step-like amplitude of water level and postseismic water level recovery rate to constrain the Skempton ratio and hydraulic diffusivity. Finally, we simulate the crustal deformation caused by postseismic poroelastic rebound based on the optimal poroelastic parameters.　　Our results show that the poroelastic parameters of the shallow crustal layer have a significant impact on the deformation characteristics of postseismic poroelastic rebound. The optimal poroelastic parameters obtained in this study can be used to simulate the deformation caused by postseismic poroelastic rebound in other areas. We also find that the time evolution of postseismic poroelastic rebound is closely related to the hydraulic diffusivity and the Skempton ratio. The hydraulic diffusivity controls the rate of pressure diffusion in the crust, while the Skempton ratio reflects the degree of coupling between the solid and fluid phases in the crust.　　Our study has important implications for earthquake prediction and hazard assessment. By considering the effects of postseismic poroelastic rebound, we can improve our understanding of the deformation characteristics of the crust after an earthquake, and develop more accurate models for predicting postseismic deformation. This can help us to better assess the risk of earthquakes and to develop more effective strategies for earthquake mitigation and disaster response.　　Our study provides a valuable case study of postseismic poroelastic rebound using groundwater level observations. The findings of this study can be used to improve our understanding of the deformation characteristics of the crust after an earthquake, and to develop more accurate models for predicting postseismic deformation. However, there are still some limitations for our study. For example, we only consider the shallow crustal layer, and the effect of the deep crustal layer on postseismic poroelastic rebound is not considered. In addition, the relationship between the hydraulic diffusivity and the Skempton ratio needs to be explored in more detail in future studies.