Quaternary deformation of the Bajo Segura blind fault (eastern Betic Cordillera, Spain) revealed by high-resolution reflection profiling

Abstract

The blind reverse Bajo Segura Fault is located at the eastern extreme of the Trans-Alboran shear zone (Betic Cordillera, southeast Iberian Peninsula). The surface expression of recent activity of this blind ENE–WSW fault is represented by coseismic surface anticlines and growth synclines on both sides of the anticlines. In the synclines, the deformation of the most recent Quaternary materials is obscured by a sedimentary unit more than 30 m thick which was deposited during the later part of the Late Pleistocene and the Holocene. The present study reports three high-resolution seismic profiles made in the northern growth syncline, which was the one developed most by the Bajo Segura Fault. In these seismic profiles we recognize the boundary between pre-growth strata and growth strata. This marker, Early Pliocene in age, dates the start of the activity of this blind reverse fault. The geometry observed in the seismic profiles of the syntectonic strata, dating from the Late Pliocene and Quaternary, indicates a limb rotation folding mechanism. On seismic profile 2, the complex geometry of the Benejúzar anticline forelimb can be attributed to several splay faults close to the surface of Bajo Segura Fault.

Quaternary active tectonic structures in the offshore Bajo Segura basin (SE Iberian Peninsula – Mediterranean Sea)

“…The age of formation of the folds was established from the analysis of successive progressive unconformities in the fold limbs, and it is not synchronous along the entire basin. For instance, the E-W folds, such as La Marina and Santa Pola anticlines, initiated their activity during the Upper Miocene, whereas the NW-SE folds, such as the Cabo Cervera anticline and the Torrevieja syncline, became active during the Pliocene (Alfaro et al, 2002a;Giménez et al, 2009 (Giménez et al, 2009). This result confirms the recent activity of the faults and folds in the Bajo Segura basin.…”

“…1), and the BSFZ (Montenat, 1977) to the south, both running approximately ENE-WSW. The BSFZ is characterized by several ENE-WSW blind thrusts that offset the Triassic basement of the Internal Zone and fold the Upper Miocene to Quaternary sedimentary cover (Montenat, 1977;Bousquet, 1979;López Casado et al, 1987;Somoza, 1993;Taboada et al, 1993;Alfaro, 1995;Alfaro et al, 2002aAlfaro et al, , 2012. The activity of these blind thrusts has produced an anticlinorium constituted by several north verging folds (Fig.…”

“…The folds are generally gentle or open with limbs usually dipping less than 30 • , although strata of the Pliocene Segura conglomerate formation are sub-vertical in the northern limb of the Hurchillo anticline (Alfaro et al, 2002a). These active growth folds are interpreted as the result of several imbricated ENE-WSW blind thrusts limited by NW-SE San Miguel de Salinas (SMSF), Torrevieja (TF) and Guardamar dextral transfer faults (Alfaro et al, 2002a). The age of formation of the folds was established from the analysis of successive progressive unconformities in the fold limbs, and it is not synchronous along the entire basin.…”

“…6). The Torrevieja syncline described onshore (Montenat, 1977;Somoza, 1993;Alfaro et al, 2002a;Giménez et al, 2009) extends offshore in a WNW-ESE direction for more than 20 km.…”

“…Nevertheless, this zone has been affected by moderate to large historical earthquakes of which the largest is the 1829 Torrevieja earthquake (I EMS98 IX-X) (López Marinas, 1976;Mezcua, 1982;Rodríguez de la Torre, 1984;Muñoz et al, 1984;Albini and Rodríguez de la Torre, 2001;Martínez Solares and Mezcua, 2002). The onshore portion of the BSFZ comprises active faults and folds resulting from the transpressive setting established in the Plio-Pleistocene (Montenat, 1977;Taboada et al, 1993;Silva et al, 1993;Alfaro et al, 2002aAlfaro et al, , b, 2012. By contrast, the offshore area is almost devoid of tectonic data (Alfaro et al, 2002b).…”