Abstract
Owing to the intense tectonic activity and significant seasonal surface mass change, Southwest China is characterized by noticeable vertical land movement. We determined the vertical movement of Southwest China using 10 years of data from 41 continuous global positioning system (GPS) stations, gravity recovery and climate experiment (GRACE), and surface loading model (SLM). The annual variation in hydrological loading is the main factor causing the seasonal oscillation of surface deformation in Southwest China. Seasonal deformations captured by GPS, GRACE, and SLM are consistent to a certain extent, and the correlation coefficients between GPS/GRACE, and GPS/SLM are 0.82 and 0.81, respectively. After deducting the results yielded by GRACE and SLM from the GPS time series, the average reductions in root mean square were 41.3% and 38.0%, respectively. However, some systematic differences were observed among the annual amplitudes and phases of the seasonal deformations among the three products. For example, the average amplitudes estimated by GRACE and SLM were 7.4 mm and 6.1 mm, respectively, which were smaller than the amplitude deduced from GPS (9.7 mm). Furthermore, mean phase delays of 16, 22, and 6 days were observed between GPS/GRACE, GPS/SLM, and GRACE/SLM. The data processing errors and local geophysical signals in GPS and the underestimation of land water storage in GRACE and SLM were jointly responsible for the systemic differences. The simulated data show that the misestimating of hydrological loading can explain approximately 50%, 64%, and 83% of the phase delays between GPS/GRACE, GPS/SLM, and GRACE/SLM, respectively. In addition, we obtained long-term vertical crustal motion rates by subtracting the loading deformation rates estimated by GRACE from the linear rates of the GPS. The vertical crustal motion in this region is block-dependent. The Central Yunnan block and its eastern boundary are uplifted; meanwhile, the Southwest Yunnan block, which features stretching in the horizontal direction, appears to be subsiding. The aforementioned results can provide data support for the study of water resource utilization and geodynamics in Southwest China.
Highlights
Southwest China (Fig. 1), which is located at the southeastern margin of the Tibet Plateau, is one of the regions with the most intense tectonic and seismic activity in Chinese Mainland due to the collision of the Eurasian and Indian plates (Royden et al 2008; Shen et al 2005; Yin and Harrison 2000)
We derived the temporal variations of different environmental mass loading components, which were estimated by surface loading model (SLM) at 41 global positioning system (GPS) stations
The results show that vertical deformation caused by non-tidal ocean loading (NTOL) (Fig. 3; green line) was the weakest, with an amplitude of less than 0.3 mm, as the research area is far from the coastline
Summary
Southwest China (Fig. 1), which is located at the southeastern margin of the Tibet Plateau, is one of the regions with the most intense tectonic and seismic activity in Chinese Mainland due to the collision of the Eurasian and Indian plates (Royden et al 2008; Shen et al 2005; Yin and Harrison 2000). The climate in this region has a subtropical plateau monsoon that is characterized by abundant precipitation with a significant annual cycle (Li et al 2015; Xiao et al 2014), resulting in the impressive seasonal oscillation of crustal loading deformation. Sheng et al (2014), Hao et al (2016), Pan et al (2018), and Zhan et al (2020) found that the seasonal vertical deformation time series acquired by GPS was highly correlated with that acquired by GRACE in this region, indicating that the annual variation of land water is the main reason for the seasonal deformation. Owing to the strong tectonic activity, long-term vertical crustal movement in Southwest China is significant. Distinguishing the crustal tectonic movement and loading deformation in the vertical GPS time series is essential to understand the present tectonic activities in this area
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