Effect of bedrock terrain on seismic ground motion

Based on theoretical analysis, the spectral element method is used to study the effect of bedrock terrain on ground motion. The achievements are as follows: (1) The intensity of bedrock ground motion is related to bedrock occurrence, incident orientation of seismic wave and other factors. The incident orientation of seismic waves is closer to the tangent direction of bedrock surface, and the intensity is smaller. On the contrary, the incident orientation is closer to the normal direction of bedrock surface, and the intensity is stronger. (2) The presence of bedrock with convex terrain leads to weakening of the surface intensity of ground motion, and thus to the formation of the relative weakening zone of ground motion intensity. While, the presence of bedrock with concave terrain leads to strengthening of the surface intensity of ground motion, and thus to the formation of the relative enhancement zone of ground motion intensity. (3) Under different bedrock topographic dips, there are different relative variation zones of ground motion intensity. Under the action of the bedrock with convex terrain, the relative weakening zone of ground motion intensity is 1.13~1.69 times larger than the bedrock convex area, which increases gradually with the increase of bedrock topographic dip. Whereas, under the action of the bedrock with concave terrain, the relative enhancement zone of ground motion intensity is 0.5~1 times smaller than the bedrock concave area, which decreases gradually with the increase of bedrock topographic dip. (4) Under different cover layer thicknesses, there are different relative variation zones of ground motion intensity. Under the action of the bedrock with convex terrain, the ratio of the relative weakening zone ground motion intensity to the bedrock convex area increases gradually with the increase of cover layer thickness. However, under the action of the bedrock with concave terrain, the ratio of the relative enhancement zone of ground motion intensity to the bedrock concave area decreases gradually with the increase of cover layer thickness.