INTRODUCTION AND PRELIMINARY ANALYSIS OF STRONG MOTION RECORDINGS FROM THE 12 MAY 2005 Ms8.0 WENCHUAN EARTHQUAKE OF CHINA*

摘要

An Ms8.0 Wenchuan earthquake occurred on the Longmenshan fault belt in Sichuan, China on 12 May 2008.The strong motion recordings of the main shock are obtained from 460 permanent free-field stations and three arrays for topographical effect and structural response observation in the National Strong Motion Observation Network System (NSMONS) of China, and a large numbers of acceleration records from the strong aftershocks occurred were also obtained by permanent free-field stations of the NSMONS and 59 mobile instruments quickly deployed after the main shock. The mobile instruments are specifically deployed to record the strong motions of the strong aftershocks for the purposes of near-fault effect, topographical effect, basin effect and structural response observation. This paper provides a detailed description of the relevant stations and the resultant strong motion measurements of the main shock, and a brief description of the mobile observation. The preliminary analysis of the recordings shows that over 1,400 components of strong motion records are obtained from the main shock. Among the records, there are more than 500 components with peak ground acceleration (PGA) larger than 10 gal, 200 larger than 50 gal, 115 larger than 100 gal, 42 larger than 200 gal, 16 larger than 400 gal, and 7 larger than 600 gal. With the stations of the NSMONS and mobile stations, over 20,000 components of acceleration records were obtained from strong aftershocks. In the aftershock records, the largest PGA has exceeded 800 gal which was recorded in the Qingchuan aftershock on 5 August 2008. Some near-fault properties of recordings are also demonstrated such as large vertical acceleration, rupture directivity effect, fault slip effect, hanging wall effect, basin effect, etc.