## 1 Introduction  
One of the goals of geodesy is to achieve and maintain reference frames from global to national scales. The implementation of the international terrestrial reference frame (ITRF) follows the basic principle that minimizes the total horizontal velocity of selected globally distributed reference stations [1]. ITRF2014 was generated for the first time in the history of the ITRF by augmented modeling of nonlinear site motion, taking into account the GNSS times series of seasonal (annual and semi-annual) signals and post-earthquake deformation at sites affected by large earthquakes [2]. It thus determines accurate and robust long-term frames and site velocities. The motion of a GNSS site relative to a global reference frame is typically dominated by the long-term crustal motion of the tectonic block where the site is located [3]. A regional or local scale reference frame is needed when researchers are interested in local scale ground deformation, which is usually aligned with the ITRF to maintain high accuracy and stability [4]. GNSS continuously operating reference stations (CORS) effectively measure the coordinate changes at reference stations, especially those located at tectonic plate boundaries [5],providing accurate position measurements relative to a specific reference system (e.g., ITRF). The final product is usually generated as present velocities to identify slight ground displacements or structural deformations over time [6]. The accumulation of data from multiple CORS sites with continuous observations makes establishing a regional reference frame possible. [PERSON] et al. established a stable Gulf of Mexico reference frame (SGOMRF2014) using more than 780 CORS sites [7], and the IAG European Sub-Committee provided the homogenized position and velocity from 3192 sites over 17 years in Europe [8]. Uzbekistan established an accurate and homogeneous datum based on ITRF2008 and a reference frame consistent with regional deformation [9]. The 26 continuously operating stations covering the Spanish part of the Iberian Peninsula and Morocco form the Topo-Iberia network, providing horizontal and vertical velocity fields [10]. China is located at the southeastern part of the Eurasian plate and is affected by the eastward subduction of the western Pacific and Philippine plates and the collision of the Indian and Eurasian plates to the west and southwest, respectively, with complex and diverse crustal motions and deformations [11]. [PERSON] et al. established an accurate contemporary horizontal velocity field of the Eurasian plate in the China region based on data from hundreds of CORS sites from 1998 to 2018 [12]. Located in southwest China, Sichuan Province is in the Himalayan-Mediterranean seismic zone and has long been subject to the thrust of the northeast Indian plate and the compressional action of the Tibetan plateau, which produces intense tectonic deformation activity and frequent strong earthquakes [13]. To properly understand the motion and dynamic mechanisms of continental tectonic deformation, accurate GNSS coordinate time series and velocity fields need to be determined [14]. GNSS coordinate time series contain linear trends, periodic terms and step offsets reflecting the plate movement. The periodic signal may originate from ground deformation due to seasonal variations in temperature, atmospheric pressure, groundwater level, surface water load, snow load and soil moisture [6]. The GNSS coordinate time series exhibits time-dependent background noise with significant spatial correlation [15]. The errors caused by the incomplete modeling in the position residuals, such as satellite orbits, environmental loading effects [16] or incorrect modeling (GNSS processing strategy), are called common mode errors (CME). CME affect the accuracy of station coordinates and velocity solutions [17] and constitute one of the largest sources of the errors in the accuracy of regional network time series [18].