Chinese nationwide earthquake early warning system and its performance during several M6.0+ earthquakes occurred in 2022-2023

As one of the most earthquake-prone regions in the world, China faces extremely serious earthquake hazards, especially for those heavily populated urban areas located near major fault zones. In order to improve the ability to prevent and minimize the risk of earthquake disasters, and to reduce the losses caused by earthquakes, China is currently building a nationwide earthquake early warning system (EEWS) with more than 18,000 seismic stations. Here, we present the recent progress of this project by describing the overall architecture of the national EEWS and evaluating the system performance during four M6.0+ earthquakes that occurred within the seismic network between 2022 and 2023. The accuracy of the source characterization for these earthquakes is discussed by comparing the continuously estimated location and magnitude with the catalogs obtained from the China Earthquake Networks Center. For each earthquake, the EEWS usually generated more than one alert, and the initial alert was created about 5~8 s after its occurrence, with excellent estimates of epicentral location and origin time. In terms of magnitude estimation, the deviation for each event was relatively large at the first alert, but gradually decreased until it approached the catalog value. However, from the point view of alerting performance, the radius of the real blind zone without warning time was about 30 km and much larger than the theoretical result, mainly caused by the releasing system not considering the epicenter distance of each terminal when issuing the alerts. Although these earthquakes revealed some limitations that need to be addressed in future upgrades, the results showed that most aspects of the EEWS demonstrated robust performance, with continuous, reliable event detection and early-warning information releasing.