We now discuss the role of earthquakes in a variety of tectonic settings and, in particular, the relative role of seismic and aseismic faulting. The stability of faulting, which has been considered only for continental fault zones, is examined for oceanic faults, subduction zones, and other tectonic settings. We also review what lessons may be learned from induced seismicity.

Introduction

In the foregoing discussion, the general principles that govern the mechanics of earthquakes and faulting were described and various illustrative examples were given. We have yet to place these phenomena within the perspective of the total tectonic process of which they form a part. Since Lyell's day it has been acknowledged that earthquakes play a role in active tectonics, but the amount of the total deformation produced by this mechanism, and the role of earthquakes in different tectonic environments is still a moot point. Seismicity often is used to deduce the tectonics of a region, so, logically, we may seek to know how much is revealed and how much remains hidden by seismology. The study of earthquakes as a tectonic component has become known as seismotectonics, which is the topic of this chapter.

It has long been known that earthquake activity is a symptom, if not the agent, of active tectonics. A global map of seismicity, as shown in Figure 6.1, reveals most of the activity deforming regions of Earth.