Site amplification effects as an explanation for the intensity anomaly in the Hanyuan Town during the Wenchuan Mw 7.9 earthquake

• Published in: Earthquake Engineering and Engineering Vibration Vol. 15; no. 3; pp. 435 - 444
• Main Authors: Liu, Hongshuai, Bo, Jingshan, Li, Ping, Qi, Wenhao, Zhang, Yudong
• Format: Journal Article
• Language: English
• Published: Harbin Institute of Engineering Mechanics, China Earthquake Administration 01.09.2016
• Subjects: Civil Engineering; Control; Dynamical Systems; Earth and Environmental Science; Earth Sciences; Geotechnical Engineering & Applied Earth Sciences; Vibration; 参数敏感性分析; 地震期; 场地放大; 峰值加速度; 建筑抗震设计规范; 放大效应; 汶川; 烈度异常; rare earthquake; site amplification; Wenchuan earthquake; high-intensity anomaly; Hanyuan Town
• ISSN: 1671-3664; 1993-503X
• DOI: 10.1007/s11803-016-0334-0

The Hanyuan Town is located approximately 200 km from the macro-epicenter of the great Wenchuan earthquake. However, it is within the only Intensity VIII zone, surrounded by a region of Intensity VI. The objective of this study was to investigate this high-intensity anomaly with respect to the site amplifications in the Hanyuan Town. The base inputs were derived from the records at a nearby strong-motion station because no records were available from the town. The characteristics of the subsurface formations and their dynamic properties at a typical site in the town were obtained by drilling, field tests and laboratory tests. Seismic response and parametric sensitivity analyses of the site were conducted using Shake 91, and the results were compared with the provisions for rare earthquakes from the Chinese Code for Seismic Design of Buildings （GBJ11-89）. The results showed that the average peak acceleration at the site during the Wenchuan earthquake is similar to the code-specified value under rare earthquakes, that the corresponding spectral accelerations for periods betwcen approximately 0.35 and 0.75 s are significantly stronger than those specified by the code and that the average amplification factor at the site is significantly higher than the mean value of the site class. These findings indicate that the high-intensity anomaly in the town was primarily caused by site amplification effects from the unique structure of the soil strata.