3.2. Seismic waves
During an earthquake, part of the energy which is stored within the deformed crustal volume surrrounding the rupturing fault is released in form of seismic waves, which propagate away from the earthquake and, depending on their energy and frequency content, can cause damage to buildings. The interaction of seismic waves with man-made structures is discussed in chapter 4. The purpose of the present section is to introduce the fundamental aspects of the generation and propagation of seismic waves. In the context of PSHA, we have to be aware of the different types of waves that can be generated from an earthquake and of some of their elementary properties. Let´s start with a simple exercise.
Exercise 3.2.1 Fig. 3.2.1 illustrates a radially symmetric wave field which propagates away from the center. Discuss the characteristics of the wavefield (e.g. the kind of motion you can identify) and the potential similarities and/or differences to the kind of waves you expect from a) throwing a stone into a pond of water, b) from an explosion, c) from the collapse of a cavity, and d) from earthquakes.
Figure 3.2.1 Illustration of radially symmetric wave propagation.
In the context of seismic waves, one can distinguish different wave types, which differ in the boundary conditions under which they develop and in the way they propagate with respect to the particle motion they cause.
.............. 3.2. Seismic waves
.............. 3.2.1. Body waves
.............. 3.2.2. Surface waves
.............. 3.2.3. Directivity and directionality of wave propagation
.............. 3.2.4. Wave propagation effects