The Study On The Correlation Between3-dimenstional Topographical Features And Strong Ground Motion Amplification Factor

The topography effect is of importance in both seismology and earthquake engineering. The field study has found the local hazard distribution is greatly influenced by the topography effect. The numerical simulation is an important tool in studying the influence of topography on the strong ground motion and thus helps people understand the distribution of seismic disaster, guide the earthquake hazard assessment and reduce the damage of the disaster.Researchers have already concluded that the geometry of the mountain influences the amplification patterns of ground motion. However these past study mainly relied on two dimensional models with simple topography shapes. In this article, our research focuses on the real topography in Lushan region. Recently this area was struck by a big earthquake and its topographical irregularity is estimated to be very high. We simulate the seismic wave propagation in three dimension based on Spectral Element Method and study the ground motion characteristics in real topography. In order to separate the topography effect, we use two computing models:One model accommodates the topographical irregularity of Lushan region, while another model’s topography is set to be horizontal. In order to reduce complexity of seismic source and traveling path, the explosive source with time function expressed in the Ricker wavelet and horizontal layered velocity structure are chosen.we simulate the velocity time history on the ground surface in each computing models, and study the topographical influence on the waveform, holding time and peak velocity of ground motion. We then calculate the amplification factor of Peak Ground Velocity from the two models, aiming to deeper understanding of the topography effect. What’s more, topographical features including ridge line and slope are used in the discussion of PGV amplification factor characteristics. Ridge line represents the mountain structure and slope quantifies steepness of the mountain. From the study of ridge line and amplification factor, we obtain their qualitative relationship. Additional, From statistics amplification factor distribution on slope, we obtained the of PGV amplification changing over slope in the sense of mean,90%and60%quantile values.At the end of this article, we process the ground velocity time history through bandpass filter and obtain the PGV amplification factor in different frequency. Then we study the topography effect changing over frequency. The result shows that as the frequency increases, the amplification of ground motion on the mountain increases and the amplification zone swifts from slope to the ridge. Additionally, we count statistically the PGV amplification changing over slope in the sense of mean,90%and60%quantile values and find out the three curves have positive correlation with slope in large frequency band.