Research of Earthquake Topographic Effect

Abstract

In this paper, the influence of topography on ground-motion intensity parameter, response spectrum, peak ground acceleration (PGA) and the ratio of response spectrum were studied based on the measured data from large scale shaking table test and observation stations in XiShan park for Wenchuan earthquake. The results show that: in the EW direction, the height do not affect PGD, SMA, VSI and HI, while V_RMS decreases slightly at the middle of the slope, the other intensity parameters increase with the increase of height. In the EW direction, the height has no influence on PGD, V_RMS, SMA, SED, A_RMS, VSI and HI, while other parameters increase as the height increase. In the UD direction, the height has no influence on SMV, PGD, V_RMS, SMV, ASI, VSI and HI, while A_RMS decreases at the middle of the slope, and the other intensity parameters increase as the height increase. Ignoring the local topographic effect, the amplitude of response spectrum increases with the increase of height at the part of short period (T1s), the part of long period (T>1s) is not effected by height. The ground motion will be amplified by local canyon topography, and the influence of local topography is larger than height. The research carried out in paper will deepen the understanding of topographic effect. 0 Preface Earthquake often cause extensive rock slope failures and various types of mass movement in mountainous areas. Catastrophic seismically-induced landsides are among the Earths most powerful geomorphic events, causing sudden and dramatic changes to the landscape, creating high risks to both infrastructures and life, and reputedly causing large economic losses. Seismic waves interacting with topography lead to amplification and deamplification of resulting ground motion. In the western mountainous areas of China, the topography is extremely complex, many large hydropower stations were built in narrow valleys and many large bridge piers were built on valleys and hillsides, so the research about topographic effect is essential to the seismic design of large-scale projects. Topographic effect is always analyzed with following three approaches: motion observation, analytical analysis and numerical analysis. The motion observation is regarded as the most efficient and common approach [1]. Long time ago, the researchers found that the intensity of buildings built on local convex topography was abnormal, in order to reveal the reason of abnormal intensity, array stations were constructed specially to study the effect of local convex topography on ground motion, some observation data were obtained. Some L-7 type strong motion seismographs were installed at the crest and foot of Kagel and Josephine mountain, California, by Lawrence L. Davis and Lewis R. West, the 2 array stations had recorded several aftershocks record of SanFernando earthquake, which occurred on February 9, 1971[. Some L-7 type strong motion seismographs were also installed at the crest, hillside and foot of Butler mountain, Nevada, to record blasting vibration in test site. In 1984, in order to observe the topographic effect of rocky mountain, 8 observation stations were installed by B. E. Tucker, five stations were placed in two tunnels with different elevation, the other three were placed at the surface of outcropped rock [. After the 1989 Loma prieta earthquake, dense array stations of seven digital and triaxial seismographs were mounted on Robinwood Ridge, which is located at 7.3km northwest of epicenter, to analyze the reason of seriously damage on high-strength buildings and cracks of ground [4,. In China, a earthquake observation station was constructed in XiShan Park, ZiGong, SiChuan province in 2007, which recorded the main acceleration time history of WenChuan earthquake perfectly, the establishment of this station offers valuable data to researchers for exploring the local topographic effect on ground motion [6]. In 2010, a research was conducted by Wang Haiyun and Xie Lili with traditional spectral ratio method, some significant conclusions were drawn about the influence of topographic effect on ground motion [7]. In this paper, WenChuan seismic wave was analyzed in time and frequency domain to explore the influence of topography on ground-motion intensity parameters, response spectrum and spectrum characteristic.