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

摘要

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. 3.7Ma), giving rise to structural rearrangement of the graben margin. Until the Late Pleistocene, it has accommodated a net slip ca. 205m, with slip rate of 0.055mm/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. 142ka 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=58-117cm; recurrence period=8.4-28.4ka; potential moment magnitude M-w=5.8-5.9. The recorded displacement since ca. 142ka BP totalizes 7.0m, with slip rate of 0.05-0.07mm/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 22ka BP.