Analysis of the Behaviour of Buildings During Earthquakes
Earthquakes are vibrations of the earth’s surface caused by sudden movements of the earth’s crust which consists of a number of thick rock plates that float on the earth’s molten mantle. The plates drift on convection currents generated by hot spots deep within the earth, and deform as they move, owing to interlocking at plate boundaries. As a result, stress builds up and when the shear stress exceeds the strength of the rock, a rupture occurs along the fault line in the rock and energy is released in the form of seismic waves. The origin of the fracture is known as the focus of the earthquake (Fig. 5.1). Two kinds of body waves are propagated from the focus. The first is the compressional or P wave, which is propagated as an expanding sphere of disturbance. The second is the S wave which is characterized by shearing distortion without any volumetric change. The point on the surface directly above the focus is called the epicentre of the earthquake. When body waves strike the free surface, they give rise to two kinds of surface wave. The first are called Love waves, and consist of a horizontal motion of the surface transverse to the direction of propagation.
KeywordsGround Motion Peak Ground Acceleration Response Spectrum Lateral Force Base Shear
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