Stability of a slope can be affected by seismicity in two ways: earthquake and blasting. These seismic motions are capable of inducing large destabilizing inertial forces. In general, three methods of analysis have been proposed for the evaluation of slopes response under such conditions.
1. Pseudostatic Method: The earthquake’s inertial forces are simulated by the inclusion of static horizontal and vertical forces in limit equilibrium analysis.
2. Newmark’s Diaplacement Method: This method is based on the concept that the actual slope accelerations may exceed the static yield acceleration at the expense of generating permanent displacements (Newmark, 1965).
3. Dynamic Finite Element Analysis: This is a coupled two or three dimensional analyses using appropriate constitutive material model that will provide details of concerning stresses, strains, and permanent displacement.
When a seismic motion occurs, different types of seismic waves are produced. The main seismic wave types are Compression (P), Shear (S), Rayleigh (R) and Love (L) waves. P and S waves are known as body waves, because they propagate outward in all directions from source (such as an earthquake) and travel through the interior of the earth. Love and Rayleigh waves are surface waves and propagate approximately parallel to the earth’s surface.
Figure 8.1: Typical seismogram ( www.geo.mtu.edu)
Figure 8.2: definition of earthquake terms (www.culcanhammer.net)