HOW CONSISTENT IS DEPOSITION AT THE BASE OF FAULT SCARPS?

Fault scarps are important archives for storing information on past earthquakes via the creation of accommodation space and subsequent deposition of sedimentary material. Such deposits can be analyzed for various purposes including determining earthquake recurrence and slip rates. The fault scarp depositional environment is often considered to be largely net depositional. In contrast to deposition, erosion and hiatal periods are often difficult to detect due to removal or non-deposition. However, recent evidence suggests that not only are periods of erosion and depositional hiatus present, but that considerable uncertainty exists on how long and frequent these periods are within and among field sites. Furthermore, whether these periods interfere with extraction of earthquake records likely depends on the relative timescale of rupture versus deposition, but remains a challenging issue. Here, we examine and review data, observations, and modeling on depositional rates and patterns in modern and ancient fault scarp depositional environments. Our review suggests that stochastic episodes of deposition, hiatus, and erosion are indeed present in certain fault scarp environments and in a manner that challenges accepted conceptual paradigms. Whether these episodes effect the extraction of earthquake histories remains an open question, but new analytical methods such as 2D portable luminescence profiling may be able to detect and support interpretations of depositional completeness. As fault scarp deposition is also tied to degradation of the scarp topographic profile over time, we additionally explore the extent to which the system can be better described with diffusive versus non-local sediment transport formulations. Preliminary results suggests that models incorporating nonlocal sediment transport models may better capture the scarp form over time, although hiatus and erosional mechanics may not be fully represented.