Present-Day Crustal Vertical Motion Around the Ordos Block Constrained by Precise Leveling and GPS Data

Abstract

Precise leveling data observed in the period of 1970-2014 around the Ordos block were collected and processed to estimate present-day crustal vertical movement. Vertical rates of 6 GPS sites were employed as a priori constraints to define the reference frame. The velocity field shows that the interior of the Ordos block moves upward at a rate of 3 mm/a as a stable block. With respect to the central Ordos, the grabens and rifts around the Ordos block are undergoing subsidence, while the northeastern and southwestern Ordos uplift at the average rates of 2 and 1 mm/a, respectively. To the southeastern margin of the Ordos block, the Weihe and southern Shanxi grabens are subsiding at the rates of 4-6 mm/ a. The subsidence of the Shanxi graben indicates that the graben is experiencing extensional movement on a long timescale. To the northwestern margin of the Ordos block, the Hetao and Yinchuan rifts are subsiding at the rates of 2-3 mm/a. A 2-D buried faulting model is used to infer the normal or reverse dip-slip rates. Our solution shows that most of the normal slip rates along the faults in the grabens and rifts are *2 mm/a.

Strain Transformation Adjacent to the West Qinling Orogen: Implications for the Growth of the Northeastern Tibetan Plateau

“…Parts of the leveling data in Hao et al (2016) are included. First-order leveling observations were also collected from the National Administration of Surveying, Mapping and Geoinformation (NASMG) resurveyed in 2013, and 500 km leveling routes in the west of the Ordos block observed in 1985/1986/1994 and resurveyed in 2017 and 2018.…”

“…First-order leveling observations were also collected from the National Administration of Surveying, Mapping and Geoinformation (NASMG) resurveyed in 2013, and 500 km leveling routes in the west of the Ordos block observed in 1985/1986/1994 and resurveyed in 2017 and 2018. Vertical velocities (Figure 2B) were calculated following Hao et al (2016), with 37 stable continuous GPS vertical velocities utilized during leveling adjustment to define the reference frame and to reduce systematic errors accumulated during leveling routes (see Hao et al (2016) for more details). Since the leveling data are sensitive to local environmental effects, such as groundwater changes and human activities (Hammond et al, 2016;Hao et al, 2016), we therefore despeckle the velocities with GPS-Imaging, which is robust against outliers, to construct a spatially smoothed VLM model (Hammond et al, 2016;Kreemer et al, 2020; Figures 3B, Supplementary Figure S1).…”

“…However, vertical crustal motions have not been thoroughly investigated, hindering further understanding of the deformation pattern in this region. Hao et al (2016) proposed a vertical velocity field around the Ordos block, which is inferred from precise leveling observations with a lack of concentration on the contemporary deformation in the West Qinling regions. Additionally, the direct explanation of leveling vertical velocities might be misleading due to the influence of local non-tectonic factors (Hammond et al, 2016;Hao et al, 2016;Hammond et al, 2019).…”

“…In this study, a vertical land motion (VLM) model is constructed using a robust imaging method (Hammond et al, 2016;Kreemer et al, 2020) and leveling observations from Hao et al (2016) with new observations from recent field work. The slip rate and locking coefficients of the West Qinling fault, the longest active fault in West Qinling orogen, are calculated with the GPS velocity field from Hao et al (2021), and our VLM model.…”

Decades of Ground Deformation in the Weihe Graben, Shaanxi Province, China, in Response to Various Land Processes, Observed by Radar Interferometry and Levelling

“…Most of the levelling data used in this study are taken from [23]. Their data sources include the network of levelling benchmarks used for seismic applications across major active faults in China (surveyed by the China Earthquake Administration, CEA) and the national levelling network of China (organised by the National Administration of Surveying, Mapping and Geoinformation, NASMG).…”