Faulting and seismic activity

This chapter traces some of the ideas and concepts leading to the current understanding of the process of faulting and earthquake generation, gives examples of engineering geology investigations contributing to that understanding, describes some engineering projects that have been strongly influenced by the process, and suggests needed research. Each of these topics is discussed in sequence.

The understanding of faulting and earthquakes and of the significance of these to engineering has developed over several centuries. John Michell in 1761 was probably the first to publish a cross section of a clearly recognizable fault (Adams, 1938, Fig. 66). Michell did not attribute earthquakes to faulting, but proposed the important idea that seismic vibrations were the result of the propagation of elastic waves in the earth (Adams, 1938). Charles Lyell (1830) emphasized the uplift and depression of land that accompanies earthquakes. He did not attribute earthquakes to faulting, but a contemporary of his evidently did, for the following statement appeared in a review of Lyell’s book (Scrap, 1830, p. 463):

The sudden fracture of solid strata by any disruptive force must necessarily produce a violent vibratory jar to a considerable distance along the continuation of these strata. Such vibrations would be propagated in undulations, which may be expected, when influencing a mass of rocks several thousand feet at least in thickness, to produce on the surface exactly the wave-like motion, the opening and shutting of crevices, the tumbling down of cliffs and walls, and other characteristic phenomena of earthquakes.

This idea was apparently disregarded, and coseismic faulting, some of which reached the ground surface, was generally considered to be the result rather than the cause of earthquakes until the time of G. K. Gilbert.