Influence of site conditions on ground motion at far field loess sites during strong earthquake

WU Zhi-jian(吴志坚)^{1, 2, 3}, WANG Lan-min(王兰民)^{1, 2, 3}, WANG Ping(王平)^{1, 2, 3}, CHEN Tuo(陈拓)⁴, SHI Hang(石航)^{1, 2, 3}, YANG Xiao-peng(杨晓鹏)¹

(1. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China;
2. Key Laboratory of Loess Earthquake Engineering, China Earthquake Administration, Lanzhou 730000, China;
3. Geotechnical Disaster Prevention Engineering Technology Research Center of Gansu Province,
Lanzhou 730000, China;
4. State Key Laboratory of Frozen Soil Engineering (Cold and Arid Regions Environmental and Engineering Institute, Chinese Academy of Sciences), Lanzhou 730000, China)

Abstract:Loess is widely distributed in China and the Loess Plateau is one of the major areas where strong earthquakes often take place. The seismic amplification effects were discovered in the Plateau during the Wenchuan Ms8.0 earthquake and some other strong events. Based on earth tremor observation, borehole exploration and site seismic response analysis, the site effects of topography of Loess Yuan on ground motion were investigated in details. The earth tremor investigation shows that predominant frequencies at the bottom sites of Loess Yuan are greater than those at the top obviously. The sites seismic response analysis shows that the Loess Yuan may amplify peak ground acceleration (PGA) by 1.44-2.0 times. Therefore, site effects of mountains and loess topography on ground motion should be taken account into in seismic design in loess regions.

Key words:earth tremor; borehole exploration; site effects; seismic response