The number and density of strong-motion observation stations in mainland China was seriously behind the number in the United States, Japan, Iran, and Mexico prior to the year 2000 (Xie et al. 1982; Gao et al. 2001; Zhou 2006; Nozu 2004). The existing accelerograph network could not meet the needs of research, engineering, and construction in China. To improve the situation, the nation provided funds to implement construction of the National Strong Motion Observation Network System (NSMONS) of China in the 10th National Five-year Plan. The project considered the existing strong-motion stations, seismicity in all regions and cities, and the distribution of major engineering structures. It also considered the research and construction needs and trends to build the NSMONS. The network focuses on regional distribution of permanent stations, stations in major cities for rapid reporting of intensity, and special arrays for special research purposes, as shown in Figure 1. The network is augmented with mobile observations and includes the National Network Center and Regional Network Centers for record recovery, processing, and dissemination; and network technical support, management, and maintenance.

The construction of NSMONS began in 2002 with five years of construction, trial operation, and inspection, and was put into formal operation in March 2008 (Earthquake Disaster Prevention and Mitigation Division of China Earthquake Administration 2008). During the Wenchuan, China, earthquake of 12 May 2008, the network system was fully operational and obtained records of the mainshock from about 460 permanent free-field stations and three arrays for topographical effect and structural response observation. After the mainshock, 59 mobile instruments were deployed in the hardest-hit areas to record motions of strong aftershocks. A large number of aftershock records have been obtained from these mobile instruments. The strong-motion records from the mainshock and aftershocks will provide basic data for …