Present‐Day Crustal Deformation of Continental China Derived From GPS and Its Tectonic Implications

Abstract

We process rigorously GPS data observed during the past 25 years from continental China to derive site secular velocities. Analysis of the velocity solution leads to the following results. (a) The deformation field inside the Tibetan plateau and Tien Shan is predominantly continuous, and large deformation gradients only exist perpendicular to the Indo‐Eurasian relative plate motion and are associated with a few large strike‐slip faults. (b) Lateral extrusions occur on both the east and west sides of the plateau. The westward extrusion peaks at ~6 mm/yr in the Pamir‐Hindu Kush region. A bell‐shaped eastward extrusion involves most of the plateau at a maximum rate of ~20 mm/yr between the Jiali and Ganzi‐Yushu faults, and the pattern is consistent with gravitational flow in southern and southeastern Tibet where the crust shows widespread dilatation at 10–20 nanostrain/yr. (c) The southeast borderland of Tibet rotates clockwise around the eastern Himalaya syntaxis, with sinistral and dextral shear motions along faults at the outer and inner flanks of the rotation terrane. The result suggests gravitational flow accomplished through rotation and translation of smaller subblocks in the upper crust. (d) Outside of the Tibetan plateau and Tien Shan, deformation field is block‐like. However, unnegligible internal deformation on the order of a couple of nanostrain/yr is found for all blocks. The North China block, under a unique tectonic loading environment, deforms and rotates at rates significantly higher than its northern and southern neighboring blocks, attesting its higher seismicity rate and earthquake hazard potential than its neighbors.

“Frame Wobbling” Causing Crustal Deformation Around the Ordos Block

“…GPS data for the study area are primarily from Phase I of the Crustal Movement Observation Network of China (CMONOC), observed in 1999, 2001, 2004, and 2007, and Phase II of the CMONOC that has been re‐surveyed once every 2 years from 2009 to 2019. In addition to the CMONOC I and II data used in previous studies (M. Wang & Shen, 2020; W. Wang et al., 2017; Zhao et al., 2017), we collected GPS data from 107 GPS stations in regional networks that have been re‐surveyed approximately every year from 2006 to 2015 by the Second Monitoring and Application Center (SMAC), China Earthquake Administration (CEA), and 185 GPS stations in the National GPS Geodetic Control Network of China (NGGCNC), which were first surveyed in 2005, 2006, or 2014, and then re‐surveyed twice by SMAC in 2012, 2015, or 2017, and 2019. As shown in Figure 1, the GPS stations from the regional networks (magenta squares) are distributed in the grabens around the Ordos block, while the stations in the NGGCNC (blue stars) are distributed in the internal Ordos block and the Qinling orogen.…”

“…We used Kriging method to interpolate the coseismic displacements following the 2008 Ms 8.0 Wenchuan, China earthquake (Shen et al., 2009) and the 2011 Ms 9.0 Tohoku‐Oki, Japan earthquake (Hao et al., 2020) to correct coseismic offsets of contaminated GPS time series. The GPS observations affected by significant postseismic deformation following the 2008 Wenchuan earthquake (M. Wang & Shen, 2020) were utilized before the main shock. For campaign‐mode GPS stations from CMONOC observed every 2 or 3 years, we only used the weighted least‐square method to fit time series without considering seasonal variations and color noise model, and estimate the linear velocity.…”

Diffuse Deformation in the SE Tibetan Plateau: New Insights From Geodetic Observations

“…We tested Wt values of 0, 6, 12, and 18 following Shen et al (2015). Values of 0 and 6 result in extremely high strain rates that deviate significantly from previous studies ( Figure S1; Kreemer et al, 2014;Pan & Shen, 2017;Wang & Shen, 2020) and, in the case of Wt = 18, high-strain regions are clearly converted to one with low strain, indicating oversmoothing ( Figure S1). In order to preserve detailed deformation characteristics and maintain consistency with published strain rates (e.g., Kreemer et al, 2014;Pan & Shen, 2017), we used a Wt value of 12 to calculate dilatational strain rates, maximum shear strain rates, and principal strain rates (Figures 3c and 3d).…”

Effects of Earthquake Recurrence on Localization of Interseismic Deformation Around Locked Strike‐Slip Faults

“…They differ from the faults in Figure 1 by having a low geological slip rate V o = 2~3 mm/year and long recurrence interval of large earthquakes of the order of T ≈ 4,000 years (Jiang et al, 2017; Yu et al, 2018). The Global Navigation Satellite System (GNSS) measurements shown in Figure 2 consist of data collected through multiple campaign surveys during 1995–2008, 1999–2015, and 2009–2015 and many continuous measurements from 1999 or 2009 to 2016 (Wang & Shen, 2020). The 6 to 17 years observation time spans allow reasonable determination of velocities despite relatively large measurement errors.…”