| Chinese continent,the most extensive and intense region of crustal deformation,is a region with the most frequent seismic activity.It is a most ideal and representative region for studying the intraplate crustal deformation and seismic mechanism.Using space geodesy technology to monitor crustal deformation is one of the most important means to study crustal deformation.Compared with the traditional methods,Global Positioning System(GPS)has the advantages of high resolution and high precision,and can obtain high-precision,large-scale crustal deformation velocity field and monitor the small dynamic changes of the crust.Especially with the construction and development of Crustral Movement Observation Network of China(CMONOC),accumulated a wealth of GPS observation data,this paper collected,collated,processed CMONOC GPS observation data,presents Chinese continent present-day crustal deformation GPS velocity field.On this basis,taking the Sichuan area as an example,we explore the possibility of earthquake prediction and block clustering analysis.The main study focus of this paper is as follows:(1)We use the Precise Point Positioning mode of PANDA software which is developed by China independently to process GPS observation data sampling at 30 s of the CMONOCI/II projects observed from 1998 to the end of 2020,and converted into the Eurasian framework of the ENU coordinate time series.The data procssed includs continuous observation data observed from 1998 to 2020 of 27 base stations of the Phase-I stations,mobile observation data observed during 1998 – 2020 of 27 basic stations of the Phase-I stations are not less then 15 periods ? mobile observation data observed during 1998-2020 of 1000 campaign stations of the Phase-I stations are not fewer than 11 periods?continuous observation data observed from 2010 to 2020 of 233 base stations of the Phase-II stations?mobile obsevation data observed during 2011-2020 of 1000 campaign stations of the Phase-II stations are not fewer than 6 periods.(2)In view of the complex causes of GPS coordinate time series,we developed the GPS time series post-processing method of comprehensive trajectory model,independent component analysis(ICA),the coseismic and the postseismic correction.Finally,we obtain the interseismic GPS velocity field in the Chinese continent including 2112 GPS stations observed from 1998 to 2020.(3)Forecasting the long-term shallow seismicity for the Sichuan-Yunnan region which is China Seismic Experimental Site based on the latest GPS velocity field calculated in this paper.It is forecasted by means of latest strain rate field and and the 1977-2016 Global Centroid Moment Tensor(GCMT)earthquake catalog and the model of SHIFT?GSRM2f that there may occur about 26 Mw6.0+,8 Mw6.5+,and 3 Mw7.0+ earthquakes every 100 years in the Sichuan and Yunnan area.The consistency test shows that the prediction results are more consistent with the GCMT and ISC-GEM seismic catalogues in different time spans,and the prediction results are close to the actual seismic catalogues and reliable.At the same time,the forcast results also show that there is still a high seismic risk in the Sichuan-Yunnan area,such as the Daofu-Kangding gap,where the deformation pattern is very complex,which can not be described by simple block model or continuous deformation model.(4)Clustering analysis is carried out to identify blocks in China Seismic Experimental Site based on the latest GPS velocity field.Cosidering the comparison of DB index and clustering effect,the Sichuan-Yunnan area is finally divided into six blocks with the method of the hierarchical clustering algorithm.The results of cluster analysis are consistent with the results of geological division.The cluster results also show that the boundaries of Longriba fault,Xianshuihe fault,Daliangshan fault,Zemuhe fault,and Xiaojiang fault are clearly identified.The contours of blocks such as the Sichuan-Yunnan Diamond,South China,southern Yunnan,Bayankala and Qiangtang are clearly described by cluster analysis. |
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