**1. Introduction**

The North-South Seismic Region in central China is one of the focal regions that pays special attention to decreasing the threat of earthquakes in China. A number of devastating earthquakes took place in this area, containing the 1920 Haiyuan M8.5 earthquake, the 1970 Tonghai *M*S7.8 earthquake, the 2008 Wenchuan *M*S8.0 earthquake, and 2013 Lushan *M*S7.0 earthquake. This seismic zone was encircled by the Ordos block, the Sichuan Basin, and the Tibetan Plateau in the tectonic backdrop [1]. The Indian plate colliding with the Eurasia plate, which caused the Tibetan plateau to rise and expand, is represented by the region's variation in crust thickness, which ranges from 30 to 46 km in the east to 46–74 km in the west [2]. There exist two

experiment sites in history, one is the West-Yunnan Earthquake Prediction Experiment Site in 1980, and another is the National Experiment Site for Earthquake Monitoring and Forecast in 2014, have both been established there because of the region's reality [3]. Following the Regional Earthquake Likelihood Models (RELM) workshop, SCEC suggested that other regions take part in the testing process for various prediction models using religious assessment methodologies. The Collaboratory for the Study of Earthquake Predictability is offering this location as one of the first testing sites in China [4, 5].

The China Seismic Experimental Site (CSES) was launched on May 12, 2018 [6–8]. Given that CSES only covers the Chinese provinces of Sichuan and Yunnan, its geographic scope is less extensive than that of the field site before it. It builds on ideas from ecology and environmental science to propose Coordinated Distributed Experiments (CDEs), a novel collaborative research strategy that follows the design for CSES [9]. As CESE work has progressed in recent years, the concepts of retrospective and prospective [10], start and trial [7], planning and test [11], earthquake forecasting, and system design [12] have been revised. At the same time, the testing facility will be built in the CSES area as part of CSEP2.0, which was also announced in 2019 [13–17]. This study will provide an overview of seismicity analysis using historical and contemporary catalogs, the nowcasting experiment, and ergodicity feature, particularly for the potential assessment prior to strong events like August 3, 2014, Ludian *M*S6.5 earthquake; October 7, 2014, Jinggu *M*S6.6 earthquake; May 21, 2021, Yangbi *M*S6.4 earthquake; and September 5, 2022, Luding *M*S6.8 earthquake. **Figure 1** depicts the geographical distribution of earthquakes in the CSES area with a magnitude greater than 6.0 from 700 B.C. to A.D. 2022.
