Study On Present-day Crustal Movement With GPS Data And Modeling The Active Deformation In The Chinese Mainland

The Chinese mainland, which is located in the southeastern part of Eurasia plate, is one of the most actively deoforming areas with significant crustal movement and widespread earthquakes, due to its contact with India plate, Philippine plate and Siberia-Mongolia subplate. Therefore, the study of the deformation of Chinese mainland is critical to understand long-term crustal deformation and dynamic processes, and has important implications for faulting mechanism and earthquake hazard assessment.In the late1980s, China began to utilize GPS measurements in order to monitor the crustal deformation. Over the next20years, several campaign-mode GPS surveys were carried out in the Tibet plateau, Sichuan-Yunan and Tienshan, etc., and abundant GPS data had been obtained since then. With the implementation and operation of "Crustal Movement Observation Network of China "(CMONOC) and " Continental Tectonic Environment Monitoring Network of China "(CTEMNC), the capability of monitoring the crustal movement and its related research has made considerable progresses in China.Nowadays, owing to the improvements for the models related to the GPS data processing and the precisions of the GPS reference frame, the new software models, new reference frame and data with much longer time span provide us the oppotunity to obtain more precise velocity field. This work utilize the GPS data mainly from CMONOC, combined with the data from CTEMNC and the published velocity field results from other research groups, in order to study the crustal movement and active deformation in the Chinese mainland. The GPS data in this study are processed homogeneously using the BERNESE GPS software, which is deferent from previously used GAMIT or GIPSY softwares. The main content and conclusions are as follows:1) Decade-long coordinate time series of26continuous GPS sites of CMONOC are analyzed for their noise content using maximum likelihood estimation (MLE). The noise properties of continuous GPS time series of CMONOC are studied for both the temporally and spatially correlated characteristics, and the velocity uncertainties of the continuous GPS sites are quantified. Besides, in addition to the annual and semiannual signals, the influence of other periodic signals on the noise assessment is also analyzed.The main conclusions are:This work study the noise properties of continuous GPS time series of CMONOC for the unfiltered, filtered solutions and also the common mode signals in terms of power law plus white noise model. In the spatial filtering, a common mode error was removed for every time series from a modified stacking of position residuals from other sites within～1000km of the selected site. The common mode signal in our network has a combination of spatially correlated flicker noise and a common white noise with large spatial extent. The common mode signal removed in the spatial filtering has a mean magnitude of0.65(north),0.72(east),1.39(vertical) mm of white noise and a mean magnitude of2.86(north),2.98(east),10.11(vertical) mm/a1/4of flicker noise, respectively. In addition, the mean of the velocity differences (and their corresponding standard deviations) obtained from the white noise plus flicker noise model between unfiltered and filtered solutions is0.04±0.09,0.06±0.15,-0.06±0.34mm/a, for north, east and vertical components, respectively, indicating an overall agreement between the velocity estimates of the unfiltered and filtered coordinate time series.Through the comparison of different noise models, we can draw that for the unfiltered solutions the main coloured noise is a flicker process; whereas for the filtered solutions the main coloured noise is a general power law noise process with any estimated spectral index. On the whole, for the unfiltered solutions, when a pure white noise model is assumed, the velocity error in CMONOC continuous GPS position time series may be underestimated by factors of8-10compared with that of the white plus flicker noise or white plus power law noise model. For the filtered solutions, when a pure white noise model is assumed, the velocity error may be underestimated by factors of8-16compared with that of the white plus flicker noise or white plus power law noise model. In addition, when using a white plus flicker noise model, the median values of the velocity errors for the unfiltered solutions are0.16,0.17and0.58mm/a for the north, east and vertical components, respectively; and the median values for the filtered solutions are0.09,0.10and0.40mm/a for the north, east and vertical components, respectively.2) The horizontal velocity field was derived using the campaign-mode GPS data from CMONOC surveyed in1999-2011and CTEMNC surveyed in2009-2011. The vertical velocity field was obtained using the campaign-mode GPS data from CMONOC surveyed in1999-2011. Besides, combined with other published results, a more complete and high resolution horizontal velocity field covering the whole Chinese mainland and its surrounding areas has also been given.Preliminary results from vertical velocity field demonstrate that most of the Chinese mainland has a low-speed vertical motions and the general trend of Tibetan Plateau is toward uplift with low rates.Specifically speaking, the GPS sites in the Qilian-Alashan of northeastern Tibet have a mean vertical rate of1.0mm/a; the GPS sites in the Himalaya and Lhasa blocks have a mean vertical rate of1.6mm/a; the sites in the western Sichuan have a mean vertical rate of1.9mm/a; the sites within the Tienshan have a low uplift trend with a mean rate of1.8mm/a; the sites within the South China and Tarim blocks have insignificant vertical rates of<1mm/a; in the North China plain, many sites show significant subsidence due to the effect of groundwater pumping, and several sites even have subsidence rates of6-10cm/a; the sites in the northeastern China have a relatively high vertical uplift rates of3-5mm/a.3) Taking advantage of the velocity field obtained above, this work refine the active block model for the Chinese mainland. To interpret the GPS velocity field, the GPS velocities are inverted simultaneously for the effects of block rotations, elastic strain induced by the block-bounding faults and the block movement and fault slip rates are calculated from this block model. Within the precision of GPS measurements, this block model provides a first-order description of the active tectonics of Chinese mainland.The slip rates inferred from this model is in a range of5-20mm/a for the major faults in Tibet and its margins and1-2mm/a in eastern China. For instance, the velocities of South China, North China plain, Dzunggar, Tarim blocks are～6.4mm/a,～4.1mm/a,～4.5mm/a and～13.1mm/a, respectively.The left-lateral slip rate for Altyn Tagh is～6mm/a; the left-lateral slip rate for Kunlun is about8-10mm/a; the left-lateral slip rate for Ganzi-Yushu-Xianshuihe is about12-15mm/a; the right-lateral slip rate for Karakorum is～7mm/a; the right-lateral slip rate for red revier is about8-12mm/a, etc.