The geological study of active faults requires a multidisciplinary understanding of several fields of earth science, including plate tectonics, structural geology, tectonic geomorphology, Quaternary stratigraphy, seismology, potential-field geophysics, geodesy, and Quaternary dating techniques. These have been described in a previous publication (Yeats et al., 1997) but are summarized here, with more recent and more detailed references.
The surface of the Earth is at two predominant levels, high-standing continents, with their mean land surface 840 m above sea level, and ocean basins, at a mean depth of 3700 m below sea level. The different levels are caused by different internal compositions of the Earth’s crust. Continents are composed of silicic granitic rocks, composed of lighter minerals including orthoclase and plagioclase feldspar and quartz, while ocean basins are composed of basalt, made of denser minerals including pyroxene and olivine, in addition to plagioclase feldspar. The boundary between these two types of crust is relatively abrupt, forming continental slopes. Granitic crust stands high with respect to ocean crust because its lower density makes it buoyant, thereby supporting high topography. Continental crust is thicker than ocean crust such that the base of continental crust projects downward, and the thicker and deeper continental crust supports its elevation above sea level, just as an iceberg rises above the sea surface because of support from the part that is submerged.