Challenges of fault characterization in areas of high anthropization. Surface variation along the Palomares Fault zone (SE Iberian Peninsula).

Abstract

The study of seismogenic faults in low deformation rate regions is a challenging task, and their correct characterization is often limited due to the action of other external processes not related to the faults. Due to their lower rates, the expression of these structures is minor and more difficult to identify compared to regions with higher tectonic rates. Furthermore, in some areas, the erosion rates can be higher than the tectonic rates and the expression of the fault can be eroded easily. Another challenge is the exponential increase of surface modification due to anthropogenic processes, related e.g. to the placement of new infrastructures or agricultural activity. Anthropic modification of the landscape due to agriculture, farming, and greenhouses land covering is extremely high in the regions of Murcia and Almeria, where the major part of the main faults of the Eastern Betics Shear Zone (EBSZ) are located. The EBSZ is a low-to-moderate strain region situated in the SE of the Iberian Peninsula, a crustal-scale transpressive fault system that absorbs a significant part of the shortening between the Eurasian and the Nubian plates. Despite its low rates, it is the most active fault system on the Peninsula. The Palomares Fault (PF) is one of the principal structures of the EBSZ, bounding to the East the main Neogene-Quaternary basins of the area. At the foot of the bounding ranges, a high level of agricultural activity has taken place on top of the alluvial deposits. Therefore, in some areas where this activity is affecting the fault expression, it is required to work with historical aerial images in order to detect erased landforms. To overcome this limitation, some digital elevation models (DEMs) have been obtained with historical aerial photos through photogrammetry, as the current DEMs are not sufficiently useful. By this methodology, it is possible to detect some vertical fault slips now affected by agricultural activity, and the variation of the surface trough time. With GIS, the two models can be compared, subtracting the photogrammetric model from the current model. The result is a map showing the areas where the surface topography has increased or decreased. This analysis has been applied in zones where fault traces have been detected by historical images, but are currently unidentifiable due to anthropogenic activity.