Tectonic Geomorphology of Normal Faults and Their Scarps

Abstract

A seismogenic fault capable of generating moderate to large earthquakes can actively displace topography repeatedly through time, and can condition surface processes helping form new landscapes. When faults rupture Earth's surface, they generally produce scarps, which are the most common landforms associated with normal faulting. The scarps are the emerged (exhumed) fault plane and are recognized as planar features, with variable dips and heights. Fault scarps can be the product of more than one earthquake and may form a complex morphology in rock or unconsolidated materials. Fault scarps generated during normal faulting of unconsolidated or poorly consolidated materials tend to have a relatively simple initial morphology. These types of fault scarps are common in alluvial fans located along mountain fronts. Such fault scarp result from horizontal tensional stress and, in frictional materials, will have initial dipangles of around 60°. However, as the initial scarp retreats, the degradation of the upper part progressively buries their base with an apron of colluvial debris at the angle of repose. The rate of the fault scarp degradation may be applied to determine the time elapsed since the burial of the initial normal fault scarp by examining the change in morphology of the scarp as its height varies along its length. Fault scarps in consolidated sediments or bedrock are preserved well in the landscape, recording evidence for individual earthquakes. Dating these faults enables the determination of short and long-term slip rates, timing of individual earthquakes, and the amount of displacement per event.