Late Holocene episodic displacement on fault scarps related to interstratal dissolution of evaporites (Teruel Neogene Graben, NE Spain)

The Mio-Pliocene formations of the Turolian type section (Teruel Graben, Spain) have sagged due to dissolution of the underlying Triassic evaporites generating a 1.7 km long monocline and accompanying synform with 130 m of structural relief. The crest of the monocline is affected by a graben that counterbalances the shortening caused by passive bending in the adjacent syncline. This graben is controlled by a master synthetic fault and a swarm of antithetic and synthetic faults with a conspicuous geomorphic expression. After acquiring Ground Penetrating Radar (GPR) profiles, three trenches were excavated in depressions associated with uphill-facing fault scarps. To our knowledge, these are the first trenches excavated across faults caused by deep-seated dissolution of evaporites. The geometrical relationships observed in two trenches indicate late Holocene episodic displacement (as many as 3 events). Some of the parameters estimated for the investigated faults are clearly different from those expectable for tectonic faults in this intraplate area. They include high apparent vertical slip rates (0.6-1 mm/yr), low average recurrence of faulting events (1.2-2 ka) and very high displacement per event values (>65 cm) for surface ruptures less then 200 m long. Our findings suggest that considering evaporite collapse faults as creeping structures is not a reliable criterion to differentiate between tectonic faults (seismogenic) and dissolution-induced gravitational faults (nonseismogenic). © 2011 Elsevier Ltd.