## 1 Introduction  
Mountain ranges, such as the Betic Cordillera in the westernmost Mediterranean, are characterized by lateral variations in crustal and lithospheric thickness due to convergence and related mountain-building processes. Consequently, much of the extensional tectonics occurring in regions with thickened crust aim to balance the excess or deficiency of gravitational potential energy [1] and are commonly referred to as gravitational collapses [2] or extensional collapses [3]. Such collapses can be synorogenic or postrogenic, depending on whether extension occurs concurrently with ongoing thickening or after mountain building, respectively [4]. Two distinct modes of flow are observed during extensional collapse: \"fixed-boundary collapse\" and \"free-boundary collapse\" [1]. In the former, extensional deformation affects the thickened regions simultaneously with the deformation of the surrounding thinner regions. The Tibetan Plateau serves as a prominent example of fixed-boundary collapse, where extensional detachment and ductile thinning of the lower crust occur alongside thrusting at the thinner boundaries [5; 6; 7; 8; 9]. On the other hand, free-boundary collapse is primarily associated with a change in plate motion, transitioning from a convergent plate boundary to a divergent plate one, as occurred in the Basin and Range Province tectonics setting (western United States and northwestern Mexico) [3; 10; 11]. The alpine Betic Cordillera constitutes the northern branch of the Gibraltar Arc, which formed in the frame of the N-S to NW-SE convergence along the E-W Eurasia-Nubia plate boundary in the westernmost Mediterranean Sea. The development of the arc since the Miocene is the result of the westward migration of the Alboran Domain driven by subduction with rollback [12; 13]. This phenomenon produced an E-W extension of the Alboran Domain in the Betic Cordillera while the collision with the South Iberian Domain was taking place [14; 15; 16; 17; 18]. Extension facilitated the exhumation of the Nevado-Filabride complex [19] below the Mecina extensional detachment with top-to-W displacement [20; 21; 22]. From the Tortonian onwards, the NNW-SSE convergence generated large E-W folds accentuating the domal structures and individualising the intramontane basins in the synclines and in the grabens [23; 24; 25; 26; 27], including the Granada Basin. Nowadays, the south-central region of the Betic Cordillera (Figure 1) is one of the most seismically active regions in the entire Iberian Peninsula [12]. Despite the NNW-SSE convergence [28; 29] both seismicity and GNSS data indicate a heterogeneous E-W to NE-SW extension affecting the shallow crust [16] west of the Sierra Nevada Dome [29; 30; 31; 32]. To the west of the Sierra Nevada, the Granada Basin extensional system (Figures 1 and 2) accommodated the E-W to NE-SW extension by high-angle normal faults over active extensional detachments [17; 18]. However, the propagation of active deformation towards the southwest and south of the Granada Basin and Sierra Nevada areas has not been adequately analysed in detail. Figure 1: Geological and tectonic setting of the Betic and Rif Cordillera forming the Gibraltar Arc. (**a**) Sketch of the western Mediterranean Alpine Mountain belts. Dark brown: onshore Alpine Belt. Light brown: offshore Alpine Belt. Blue: Cenozoic oceanic crust. BC: Betic Cordillera. RC: Rif Cordillera. (**b**) Simplified geologic map of the Gibraltar Arc. Seismicity since 1980 and M > 2.5 taken from IGN [33] and GNSS data [31; 34] are shown. Red arrows show the Eurasia-Nubia convergence [28], and blue arrows represent the extension of the central Betic Cordillera [29]. GBB: Guadix-Baza Basin. AIC: Alpujarras Corridor. CdD: Campo de Dalias. TASZ: Trans-Alboran Shear Zone. EBSZ: Eastern Betic Shear Zone. ESGB: Extensional system of the Granada Basin. ZF: Zafarraya Fault. PF: Padul Fault. BIF: Balanegra Fault. BzFZ: Baza Fault Zone. ATFZ: Almeria Tabernas Fault Zone.