Study And Application Of Poroelastic Effect In Postseismic Deformation And Induced Earthquakes

The earthquakes have caused huge economic losses and casualties from all over the world.With the development of society,people have paid more and more attention to natural earthquakes and induced earthquakes.The earthquake itself needs to go through three stages of seismic preparation,rupture and post-seismic adjustment,in which the poroelastic effect related to the underground fluid has significant influences on the post-seismic process and the stress disturbance that lead to earthquakes.Therefore,in order to better understand the process of the post-seismic adjustment and the stress disturbance mode leading to earthquakes,we need to have much deeper understanding of the mechanism of poroelastic rebound in the post-seismic process and the induced earthquakes.With the continuous improvement of observational methods and theoretical simulation,as well as the urgent surge of induced seismic events associated with industrial production,it provides abundant data for us to study the post-seismic processes and induced mechanisms related to underground fluids.Although fluid-related poroelastic rebound has long been studied as a mechanism of post-seismic deformation,few studies have been done on it in the analysis of post-seismic stage.In particular,there is still a lot of unknowns about the specific spatial and temporal distribution characteristics and response intensity at different post-seismic stages of subduction zone earthquakes.In addition,induced seismicity related to fluid injection has been extensively studied,but there are few coupling analyses for different behaviors in the production process of fluid injection and pumping coexistence,and many corresponding induced seismicity mechanisms are not clear.Therefore,we combined spatial geodesy and poroelastic deformation theory to study the poroelastic effect and gravity change induced by fluid injection and pumping,poroelastic rebound caused by natural earthquakes in subduction zones,and induced earthquakes related to fluid injection and pumping.The main achievements of this work are as follows:1.It introduced the governing equations of poroelastic theory:the equilibrium equation and conservation equation(Storage equation),and the analytical method of formula derivation under the boundary condition of dislocation and fluid injection and pumping.In the process of derivation of physical quantity changes caused by fluid pumping,an idea of simulating corresponding gravity changes is further put forward,and it is attempted to combine with surface gravity monitoring instrument.In today’s environment where GRACE satellites are widely used to capture large-scale and long-term gravity changes,real-time gravity changes in small areas combined with ground-based gravity observations such as the superconducting gravimeter(SG)may provide a good complement and validation.2.Large earthquakes can alter regional groundwater pressure,resulting in fluid flow,and the process of restoring hydrostatic equilibrium would in turn lead to observable surface deformation,termed poroelastic rebound,which is one of the most important post-seismic mechanisms for stress transfer and triggering.To constrain the poroelastic contributions to the early post-seismic deformation,we modeled the hydrologic response within 1.5 months following the 2015 Mw 8.3 Illapel earthquake and removed its effects from the observed geodetic signals.Results demonstrate the post-seismic fluid-flow patterns from the co-seismic high-slip region to the north and south sides.And the poroelastic effects in the northern side are remarkably stronger than those on the southern side,which is verified by northern liquefaction phenomena.Therefore,previous pure afterslip models overestimated the asperities on both flanks of the coseismic rupture zone and underestimate the middle region,with local errors of more than 50%.It highlights the importance of considering the poroelastic effects,when modeling the transient post-seismic deformation.In the next step,considering the multi-source hydrological observation data after the earthquake,the model of lateral heterogeneity will be established to better analyze the post-seismic adjustment process.3.A sharp increase in seismicity related to human activity in past decades has become a global problem that needs to be solved urgently.However,the detailed mechanism is still not well understood,which requires further verification.Herein we compiled the geological,industrial data,and seismic record within the Changning salt mining zone,Sichuan Basin,China,and simulated the spatiotemporal evolution of pore pressure and poroelastic stresses based on a physics-based linear poroelastic model.Our results reveal that the regional induced seismicity is driven by the pore-pressure diffusion,but is suppressed by pumping operations.We proposed a theoretically feasible strategy to arrange extraction wells around injection wells to mitigate the future seismic potential.Hence,our model could advance the understanding of physics and hazards associated with the induced earthquake in Changning and elsewhere,and help design or guide operations.Then the method of reducing the induced seismic risk would be further improved by considering the regional fault system distribution and stress accumulation.