Fault Steps

Fault steps are features similar, in many ways, to fault bends. Just as fault bends are either left bends or right bends, fault steps are either left steps or right steps. They generally create local compression or extension much like fault bends. However (as shown in the image to the right), in an area with a fault step, the main trace of the fault does not change trend. It merely "steps" over, sideways, and continues along a similar trend. For this reason, fault steps are typically small-scale features, and their effects are limited to the immediate area near the step-over. No fault step even comes close to causing the sort of effects the "Big Bend" of the San Andreas does.

This does not mean that fault steps are not important, nor does it mean they are not the subject of study and debate. Fault steps create landforms which can be used to study past movement along the fault zone, as shown at left, along a hypothetical right-lateral strike-slip fault. While convergent steps create compression and uplift, more geologists find value in divergent steps. These fault steps often create small "pull-apart" basins and sag ponds in which organic material, which can be radiocarbon-dated, piles up. When a major rupture happens, these sediments can be cut and offset, then overlain by more sediment, until the next rupture cuts those. In this manner, a chronological record of major ruptures can be preserved.

Fault steps also affect the progression of major ruptures. Some ruptures progress through fault step-overs; others are stopped. Knowing more about the ease with which fault rupture can "jump over" fault steps would help assess more accurately the risk of major ruptures along certain fault zones. Unfortunately, determining which fault steps allow and which prevent continuous rupture is still a matter of guesswork. With further studies into the nature of fault steps, we may one day have a better understanding of the role they play in rupture progression.