Research On Viscoelastic Interseismic Deformation And Locking Depth In The Himalayan Subduction Zone

The Himalayan subduction zone is located at the front edge of the collision zone between the Indian and Eurasian plates,and is the natural tectonic boundary between the Tibetan Plateau and the Indian plate.As the largest continental subduction-collision zone in the world,the Himalayan subduction zone has been a natural laboratory for studying a series of geological mechanisms such as the coupled basin-mountain system and deep material transport,and has always received much attention from the geological community.Recent studies have shown that the shallow tectonic motions(interseismic crustal deformation)in ocean-land subduction zones are to some extent controlled by the deep viscoelastic circles in the region,but the mechanisms linking the deep dynamics and interseismic crustal deformation in land-land plate subduction zones are not yet well understood.Therefore,based on the viscoelastic Earth model,an in-depth study of the influence of the deep viscoelastic medium on the interseismic deformation field in the Himalayan subduction zone is significant for the study of the dynamics of the Tibetan Plateau and the understanding of global plate motion.The study of the characteristics and distribution of fault locking can effectively estimate the pattern of seismic activity and provide an important scientific basis for early warning of geological hazards and disaster prevention and mitigation.Based on these,this paper investigates the correlation mechanism between the deep viscoelastic medium and the interseismic deformation in the Himalayan subduction zone and its influence on the depth of fracture zone closure using the regional interseismic GNSS velocity field as a constraint and a finite element numerical simulation method.The main work is divided into the following points:(1)We collected and integrated multiple sets of GNSS deformation data within the research area and transformed them into a GNSS velocity field in the Eurasian reference frame.and constructed a two-dimensional finite element model for the Himalayan subduction zone.When simulating interseismic surface deformation rates using the backslip model,the main differences between the viscoelastic and elastic models were concentrated in the horizontal displacement rates in the central and far-field regions,with the viscoelastic model exhibiting larger displacement rates.However,in terms of vertical displacement rates,the viscoelastic model showed greater uplift rates for the subducting plate model.For the subducting plate model,the main differences between the elastic and viscoelastic models in horizontal displacement rates were concentrated in the near-field region of the Main Himalayan Thrust(MHT)fault.The average vertical rates for the elastic model were slightly higher than those for the viscoelastic model,which may be related to creep along deep fault planes in the lithosphere under this kinematic model.When comparing the differences between the two models,the backslip model and subducting plate model exhibited high consistency in horizontal displacement rates under the elastic model.The main differences were mainly reflected in the vertical rates beyond 250 km.When using the viscoelastic model,the differences were mainly reflected in the near-field horizontal direction and the far-field vertical direction beyond 300 km.(2)A 3D finite element method was used to estimate the interseismic locking depth of the elastic-viscoelastic model of the MHT fault,and The RMS(root mean square)value between the GNSS velocity field and the simulated velocity field was used to assess the optimal interseismic locking depth for the elastic and viscoelastic models.The RMS was 0.79mm/yr for the elastic model at approximately 28 km and 0.79mm/yr for the viscoelastic model at 26 km.Compared to the elastic model,the viscoelastic model is a better fit for the interseismic surface,The model is a better fit for interseismic surface deformation than the elastic model.This paper presents a detailed analysis of the effects of the elastic-viscoelastic model on interseismic deformation in the Himalayan subduction zone.The differences between the two kinematic models are analysed in detail.This paper also combines the interseismic GNSS velocity field to constrain the interseismic locking depth of the MHT fault.The results of this study provide a reference for further research on the deformation mechanism of the plateau and early warning of geohazards.