Role of transverse structures in paleoseismicity and drainage rearrangement in rift systems: the case of the Valdecebro fault zone (Teruel graben, eastern Spain)

Abstract

The E–W trending, nearly pure extensional Valdecebro fault zone is a transverse structure at the central sector of the N–S Teruel graben. It was activated by the Late Ruscinian (Early Pliocene, ca. 3.7 Ma), giving rise to structural rearrangement of the graben margin. Until the Late Pleistocene, it has accommodated a net slip ca. 205 m, with slip rate of 0.055 mm/a. Paleoseismicity has been analysed in a 29-m-long, 5-m-deep trench excavated through a fault branch that offsets a Pleistocene pediment surface. The paleoseismic succession includes a minimum of 6–7 events occurred since ca. 142 ka BP, although a model with 12 events could be more realistic. The following paleoseismic parameters have been inferred, assuming a minimum of 6 and a maximum of 12 events: average coseismic slip = 58–117 cm; recurrence period = 8.4–28.4 ka; potential moment magnitude Mw = 5.8–5.9. The recorded displacement since ca. 142 ka BP totalizes 7.0 m, with slip rate of 0.05–0.07 mm/a. Slip on the transverse Valdecebro fault zone has critically contributed to bulk deformation under a prevailing ‘multidirectional’ extensional regime. Drainage patterns have been rearranged, recurrently switching between westward and southward directions as a consequence of diverse slip episodes at the Valdecebro fault zone (E–W) and the neighbouring La Hita (N–S) and Concud (NW–SE) faults. The ultimate westward drainage of the Valdecebro depression incised and dismantled a southward-sloping Pleistocene pediment sourced at the Valdecebro mountain front, representing a capture by the Alfambra river occurred between 124 and 22 ka BP.