Effects Of Inclusion And Topography On Ground Motion

Complex site such as basin, local irregular topography and underground inclusion may have remarkable influence on the ground motion, and building site selection and seismic fortification attach more and more importance to the amplication effects. This paper studies how the underground circular inclusion, typical canyon and protruding topography affect the ground motion under two-dimensional SH wave incidence. Combining with Lushan earthquake strong motion records, we analyse the effects of local irregular topography. Specific research works include:1. The dimensionless parameters of the model are introduced, and the feasibility of the model dimensionless is verified by numerical simulation.2. The influence of cavity, soft inclusion and hard inclusion on the ground motion is studied in time domain and frequency domain by using two-dimensional finite element method and spectral ratio method. Research shows that the soft inclusion and cavity have large amplification on ground motion, the rules of surface amplification are similar, and the location of surface amplification are the same, whereas the soft inclusion is more sensitive to the incident wave frequency, with a larger amplification factor. The hard inclusion is mainly expressed as a barrier, and the effect of hard inclusion is negligible.3. The influence of canyon and protruding topography on the ground motion under vertical and oblique incidence is studied in time domain and frequency domain by using two-dimensional finite element method and spectral ratio method, and the law of the influence of canyon and protruding topography on the ground motion by the change of depth-width ratio and depth-height ratio is also analyzed. Research shows that the canyon topography has relatively small amplification on the topographic points, and large amplification on near plane ground points. Under oblique incidence, the corner point of the front side of the incidence wave has the maximum amplification. As the increase of depth-width ratio, topographic amplification increases. On the contrary, protruding topography has large amplification on the topographic points, and small amplification on the near plane ground. Under oblique incidence, the topographic area where the incident wave can direct access has the maximum amplification, near plane ground area of the front side of the incidence wave take the second place, and near plane ground area of the other side of the incidence wave and the topographic area where the incident wave cannot direct access along with corner points have relatively small amplification. Under vertical incidence, the vertice of the protruding topography has the maximum amplification. As the height-width ratio increase, amplification on vertice of the protruding topography increases, whereas the amplification on the remaining points increase first and then decrease.4. Combining with strong motion records of Lushan main shock and 41 times aftershocks from four adjacent stations which are on different terrain, we use the traditional spectral radio method(RSM) and the horizontal and vertical components spectral ratio method(HVSR) to analyse topographic effect. Research shows that all the four stations are enlarged by topography. The analysis of the aftershock records shows that topographic amplification effect on 51 BXZ station which located on hillside is bigger than on 51 BXD station which located on hill foot. The 51 BXZ station has abvious amplification around 3 Hz, and 8-14 Hz some amplification. The 51 BXD station has relatively small amplification in the range of 5-10 Hz. The amplitude of the main shock record of 51 BXZ station is less than 51 BXD station may be caused by soil nonlinear effects of large earthquake.