Experimentally, particle acceleration in structures is found to provide a fairly good general index of probable damage. If one considers an elastic wave progressing through an extended medium, the stress in the medium is directly proportional to the particle velocity. The relation depends on the elastic modulus of the material, but since there is a rough correlation between elastic modulus and elastic limit it may be expected that particle velocity will be a good general index of damage in the medium. This is borne out by the experimental observation that there is a very close correspondence between structural damage and the particle velocity in the portion of structure in closest contact with the soil. Figure 2 shows horizontal and vertical components of particle velocity in basement ways and their relation to the occurrence of damage.
Velocity is recommended as the most consistent index of the probability of damage.
There is rarely a clear distinction between damage from blasting and damage from other causes. Prior inspections are strongly recommended whenever there is a chance that blasting vibrations will approach the damage threshold. The first damage generally occurs in the basement wall nearest the explosion. The degree of involvement of the rest of the structure depends on the size of the charge and its distance from the structure. As the distance increases there is, of course, a corresponding increase in the charge required to produce damage, and as the charge increases the duration of the disturbance also increases.