The Baza Fault: a major active extensional fault in the central Betic Cordillera (south Spain)

Abstract

In the Guadix-Baza Basin (Betic Cordillera) lies the Baza Fault, a structure that will be described for the first time in this paper. Eight gravity profiles and a seismic reflection profile, coupled with surface studies, indicate the existence of a NE-dipping normal fault with a variable strike with N-S and NW-SE segments. This 37-km long fault divides the basin into two sectors: Guadix to the West and Baza to the East. Since the Late Miocene, the activity of this fault has created a half-graben in its hanging wall. The seismic reflection profile shows that the fill of this 2,000-3,000 m thick asymmetric basin is syntectonic. The fault has associated seismicity, the most important of which is the 1531 Baza earthquake. Since the Late Tortonian to the present, i.e. over approximately the last 8 million years, extension rates obtained vary between 0.12 and 0.33 mm/ year for the Baza Fault, being one of the major active normal faults to accommodate the current ENE-WSW extension produced in the central Betic Cordillera. The existence of this fault and other normal faults in the central Betic Cordillera enhanced the extension in the upper crust from the Late Miocene to the present in this regional compressive setting.

Active extensional faults in the central-eastern Iberian Chain, Spain

“…In contrast, results from the Pleistocene record show how the Concud fault is noticeably more rapid. Slip rates at the Concud fault are comparable to those calculated for normal faults of the Betic Chains, as the Granada (0.03-0.38 mm/y; Sanz de Galdeano et al, 2003), Ventas de Zafarraya (0.3-0.45 mm/y during Holocene times; Reicherter et al, 2010), or Baza fault (0.12-0.33 mm/y; García-Tortosa et al, 2008;Alfaro et al, 2008). In contrast, the Concud fault moves at higher rates than El Camp fault (0.02 mm/y; Masana et al, 2001).…”

Main active faults in the Granada and Guadix-Baza Basins (Betic Cordillera)

“…Several faults might be connected, as they are geometrically aligned, but we lack firm evidence of this basin is divided in two sub-basins according to its sedimentary facies, the Guadix sub-basin to the west, which is largely filled with fluvial sediments (Viseras, 1991), and the Baza sub-basin to the east, with a predominance of lacustrine sediments (Vera 1970). This distribution is due to the tectonic control of the Baza Fault (Alfaro et al, 2008;García Tortosa et al, 2008a). This fault is the limit between the two sub-basins and its movements caused the subsidence of the hanging wall, with the development of a large lake in the eastern part of the basin (the Baza sub-basin) that existed till the late Pleistocene.…”

“…The longer term vertical displacement has led to the development of a 30 km long mountain front. Alfaro et al (2008), taking into account the total throw of the fault from the late Miocene (ranging from 2000 to 3000 m) and the dip (between 45 and 60º), deduced a vertical slip rate of 0.22 -0.37 mm/yr. This fault, the largest in the basin, was probably responsible for the 1531 Baza earthquake (Fig.…”

“…The Baza Fault zone (Alfaro et al, 2008;García Tortosa et al, 2008a) is a 37 km long normal fault (Figs. 3 and 6).…”

“…1). This area is characterized by: (1) the lowest minimum Bouguer anomaly values in the entire Betic Cordillera and a crustal thickness between 34 and 38 km (according to Banda et al, 1993); (2) the highest relief of the Iberian Peninsula as well as the maximum uplift rates of 0.5 mm/year in Sierra Nevada (Sanz de Galdeano and López Garrido, 1999;Braga et al, 2003;Sanz de Galdeano and Alfaro, 2004) and the highest fluvial incision rates (Pérez-Peña et al, 2009a;2009b); (3) notable depocentres, such as that of the Pinos PuenteSanta Fe, with Tortonian marine deposits located 1200 m below sea level in the Granada Basin (Rodríguez-Fernández and Sanz de , and other similar ones located in the Baza sub-basin (Alfaro et al, 2008); (4) the last destructive earthquake in the Iberian Peninsula, the well-known 1884 Andalusian earthquake; (5) the highest instrumental seismicity rate of the Iberian Peninsula Sanz de Galdeano et al, 2003;Sanz de Galdeano and Peláez, 2011), and (6) the highest seismic hazard of the Iberian Peninsula, according to the Spanish Building Code. The last three points pertain to the Granada Basin.…”