Recalling the concept of composite joints, it is easy to relate to composite small faults illustrated in a series of photographs and maps in Figure 1 from the Bays Mountain anticline, northwestern Tennessee (please see the Bays Mountain case study link). Figure 1(a) shows a series of calcite filled fault surfaces delineating the individual fault segments altogether defining a composite fault. Figure 1(b) is a cross sectional view of a similar structure showing multiple echelon segments sub-parallel bedding, which control the dilation and localized calcite precipitation at the stopovers. Figure 2 illustrates a composite right-lateral strike-slip fault with 40 cm slip as seen on a sandstone pavement.

Figure 1. Composite thrust faults in carbonaceous mudstone rock cropping out along a road cut, Bays Mountains, NE Tennessee. (a) Patches of calcite precipitation on a thrust fault surface. (b) Isolated calcite rhombs between a simple array of echelon thrust faults in cross section. (c) A composite fault with highly overlapping multiple fault segments bounding individual calcite veins in cross section. From Ohlmacher and Aydin (1995).

Figure 2. A composite right-lateral strike-slip fault with a slip magnitude of 40 cm as seen on a pavement of the Ross Sandstone platform, County Clare, southwestern Ireland. Note the elongated bodies of quartz in pull-aparts between right stepping fault segments. From Nenna and Aydin (2011).

Figure 3 is a larger scale example of a similar case in alternating units of fractured siltstone and deformed shale units based on the seismic interpretations of a series of normal fault segments in the subsurface. Figure 3(a) is an incipient normal fault zone illustrating faulted sand units. Obviously, here the ductility of the shale units plays a crucial role as discussed under faulting of alternating brittle and ductile multilayers. However, the faults in sands on both sides of each shale unit are mechanically communicating which is why the product is a composite fault rather than a series of independent small faults in different units. Figure 3(b) represents a more mature fault zone with highly overlapped fault segments (numbered for reference in the figure - also see 'Faulting by Shale Smearing').

Figure 3. (a) Seismic image interpretation of a series of normal fault segments in a sand-shale sequence in the Niger Delta. The collection of the segments on the left is identified as a simple composite fault. A highly developed fault zone and the segments therein are on the right side of the seismic image. (b) Highly developed zone of composite faults in sand-shale sequence in the subsurface in the Niger Delta. From Koledoye et al. (2003).