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Franck Audemard, FUNVISIS (Venezuela)
Reinaldo Ollarves, FUNVISIS (Venezuela)
Luz Maria Rodriguez, FUNVISIS (Venezuela)
Roberto Wagner, Total (Venezuela)
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This contribution discusses a set of particular landforms and drainage anomalies as reliable indicators of present-day activity of blind thrust faults in regions under humid tropical conditions, such as in Venezuela. Their identification results from studying several Venezuelan regions, all pertaining to either fold-thrust belts with different degrees of activity (Perijá, Mérida Andes, Central Interior and Eastern Interior ranges, from west to east) or a transpressional section of a major strike-slip fault (Oca-Ancón fault system). Besides, testing of these superficial indicators among the different case studies was also performed. When subsurface data was available, these morphologic indicators were correlated to their causative underlying geologic structure, to strengthen their validity. The two most significant outcomes from this investigation are: 1) the application of these criteria requires that they must comply with persistency and consistency among them. In other words, any of these single features on its own is generally insufficient to prove the activity of an underlying blind thrust fault, with few rare exceptions (e.g., flexural scarps); and 2) the second-order rivers or streams are better indicators of underlying tectonic activity. This is strongly linked to the constant competence between tectonic rates and erosion/sedimentation rates; the latter issue being controlled by stream power and sediment load.
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