Explorating Mechanism Of The Regional Surface Deformation And The Deep Tectonic Signals Using High-Precision GNSS Vertical Solutions

Time series of Global Navigation Satellite System(GNSS)station coordinates contain various deformation informations from the surface to the deep of the earth.However,limited by the technical characteristics of GNSS and various error factors,the accuracy of the vertical component is usually 2-5 times lower than that of the horizontal component.This greatly limits the research applications of vertical component.In recent years,with the accumulation of GNSS data analysis experiences and the improvement of the accuracy of error factor correction models,the current GNSS vertical component accuracy can reach 3 mm,which is sufficient to provide geodetic observational evidences for studying the deformation mechanism from the Earth's surface and deep interior.To study the deformation mechanism,two typical regions,the reclamation area in Shanghai Pudong of China,and the Mendocino triple junction(MTJ)region in northern California of the United States are selected.Based on the high-precision regional coordinate reference frame and the monitoring data of the GNSS continuous and mobile stations in these areas,the high-precision GNSS station coordinates vertical component time series and velocity field in these areas are obtained,with most of the systematic errors including nonlinear trend,Common Mode Error(CME)are removed.Following is a brief summary of the study.1.For the Shanghai Pudong reclamation area,8 mobile stations and one continuous GNSS station were used to monitor the regional surface deformation.High-precision,high-stability regional coordinate frames are established by using 5 GNSS stations of SHCORS(Shanghai Continuously Operating Reference Station)and 35 high-precision ITRF stations globally distributed.Based on the high-precision regional coordinate reference frame,the time series of the vertical component of the station coordinates are obtained,and the surface deformation caused by the known geophysical mechanism are removed by time series analysis using the software QOCA.Through the analysis of GNSS station coordinates vertical component time series,i.e.,comparison between the time series and models,the deformation mechanism in Shanghai Pudong reclamation area is probably the consolidation settlement of the artificially filled soil,and the regional filtering can cause the vertical signal due to the consolidation settlement mechanism to be eliminated as Common Mode Error.Combined with the vertical time series measured by GNSS and the consolidation settlement mechanism of the dredger fill under self-weight,a regional settlement prediction model was established to predict the settlement trend of different filled areas.The research work shows that the GNSS high-resolution vertical component can be used to infer the deformation mechanism of the regional surface deformation,and it has broad application prospects in monitoring and predicting land subsidence in the reclamation area.2.The MTJ region of Northern California is a hotspot for many scientists to study the deep tectonic movement of the Earth.The slab window in the south of MTJ is an excellent natural laboratory for studying the viscous dynamic coupling between crust and asthenosphere flow.The Mendocino Crustal Conveyor(MCC)model proposes a recognized mechanism for regional surface deformation,that is,the viscous dynamic coupling between the bottom of the North American plate and the inflowing asthenosphere flow in the southern slab window of MTJ is the main impetus for rapid surface deformation in this region.However,this model has not been able to be verified by the space geodetic observation in the past.This research work uses the Plate Boundary Observatory network(PBO)to monitor the regional surface deformation,and obtains the high-precision vertical velocity field in the MTJ region.By innovatively projecting the three-dimensional GNSS monitoring vertical velocity field onto the MCC model profile along the simulated orientation of the slab window,the CGPS measured uplift rates are in good agreement with the MCC prediction,when the projection angle is about 41°~45° with the MCC model profile line.Thus the high-precision GNSS vertical velocity field not only can successfully verify the MCC model but also infer that the flow direction of the asthenosphere material in the slab window,which is parallel to the symmetry axis of the region of thickened crust.