## 2 Overview of the Study Area  
The southeastern region of the Tibetan Plateau, located in the southern section of the North-South seismic belt of the Chinese mainland, is subject to intense compression and collision between the Indian plate and the Eurasian plate, making it an area of unique neotectonic movement with complex deformation and intense fracture activity [30; 46; 47]. Owing to the active faults in the area, a number of strong earthquakes have occurred since the beginning of the 20 st century, e.g., the Ms7.8 Tonghai earthquake in 1970, Longling Ms7.4 earthquake in 1976, Gengma Ms7.6 earthquake in 1995, Lijiang Ms7.0 earthquake in 1996, Wenchuan Ms8.0 earthquake in 2008, Lushan Ms7.0 earthquake in 2013, and Jiuzhaigou Ms7.0 earthquake in 2017. Therefore, the study of terrestrial time-varying gravity data in this area is helpful for analyzing the variation characteristics of the density of the underground medium, reflecting its dynamic tectonic implications, and exploring the seismogenic structure.  
Following the Wenchuan Ms8.0 earthquake in 2008, the China Earthquake Administration advanced the construction of its terrestrial gravity observation network to obtain high-precision and large-scale seismic precursor gravity variations before the occurrence of strong earthquakes. Thus, a hybrid gravity survey network in the southeastern Tibetan Plateau covering all major fault structures and under the control of AG stations has been established (Figure 1). The distribution of the survey network is not uniform owing to the topographic limitations. And there are approximately 19 absolute gravimetric stations and 537 relative gravimetric stations. No fewer than 500 gravity segments are repeatedly observed in each survey period. Each campaign has duration of approximately 90 d and spans approximately 12\({}^{\circ}\) of longitude and 13\({}^{\circ}\) of latitude. Generally, no fewer than two relative gravimeters are used simultaneously in a survey campaign: two CG-5 gravimeters (#1169 and #1170; hereafter, CG-169 and CG-170, respectively) are usually used in Yunnan and two LCR-G gravimeters (#149 and #150; hereafter, LCR-149, and LCR-150, respectively) are used in Sichuan.  
The GD distribution of adjacent station pairs is shown in Figure 2. The maximum GD in Sichuan is approximately 390 mGal (\(10^{-5}\) m/s\({}^{2}\)), the maximum GD in Yunnan is approximately 305 mGal, the minimum GD of the entire survey network is \(<\)100 uGal, and the average GD is approximately 60 mGal. Generally, the distance between two adjacent stations is of the order of several tens of kilometers, and road vehicles are used to travel between stations to perform observations that typically have a time interval of several hours. To remove the influence of seasonal rainfall changes, survey campaigns are accomplished semiamually (generally starting in March and July each year).  
Figure 1: Tectonic background and gravity survey network of the southeastern Tibetan Plateau. (**a**) Distribution of gravity survey network, the blue dots are the relative gravity stations of Yunnan (YN) gravity network, the pink dots are the relative gravity stations of Sichuan (SC), and the red squares are the absolute gravity stations. (**b**) Tectonic background and historical earthquakes (Since 1908). Red lines represent the main active Faults (XSHF: Xianshuihe Fault; GYF: Ganzi-Yushu Fault; LMSF: Longmenshan Fault; ANHF: Anninghe Fault; ZMHF: Zemuhe Fault; XJHF: Xiaojinhe Fault; JJF: Xiaojiang Fault; QJF: Qujiang Fault; RRF: Red River Fault; JSJF: Jinshajiang Fault; LCJF: Lancangjiang Fault). (**c**) The purple rectangle is the geographical location of the study area. (WCB: West Region Block; NAB: Northeast Asia Block; NCB: North China Block; SCB: South China Block; TPB: Tibetan Plateau Block; CBB: China-Burma Block).  
Figure 2: Distribution of gravity difference (GD) between adjacent station paris on the southeastern Tibetan Plateau (size of blue circle represents different GD, unit: mGal).