Geomorphic signature of segmented relief rejuvenation in the Sierra Morena, Betic forebulge, Spain

Abstract

Abstract. The foreland relief of alpine orogenic belts is often rejuvenated due to the intraplate propagation of orogenic deformation. Thus, in these long-lived areas, the localisation of relief rejuvenation may be largely controlled by the reactivation of previous mechanical discontinuities. In this regard, we explored the relationship between the relief rejuvenation pattern and the distribution, geometry, and kinematics of faults in a wide segment of the Betic foreland (Sierra Morena, southern Spain). Specifically, we focused on the forebulge, a WSW–ENE flexural relief that formed, paired to the Betic foreland basin, in response to orogenic load. For this purpose, we applied both qualitative and quantitative geomorphological tools, including geomorphic indices and knickpoint pattern modelling in χ space. We found that the pattern of relief rejuvenation responds to large-scale flexural uplift coupled with the tectonic activity of two groups of faults that often show evidence of reactivation, namely overall WSW–ENE faults contributing to both regional NNW–SSE relief segmentation and vertical extrusion of the forebulge, and NW–SE reverse faults associated with an outstanding WSW–ENE topographic segmentation in the west of the study area. In addition, our knickpoint modelling suggests that the faults related to the southernmost Sierra Morena mountain front have been particularly active in recent times, although their activity span and the relative uplift that they accommodate differ along the Sierra Morena/foreland basin limit. The knickpoint pattern also suggests a significant reorganisation of the analysed drainage basins. The strain partitioning accommodated by the structures involved in relief rejuvenation suggests the intraplate propagation of the transpressional deformation reported from the Betic external fold and thrust belt.

Archaeoseismological Evidence of Seismic Damage at Medina Azahara (Córdoba, Spain) from the Early 11th Century

“…In addition, recent geomorphological studies reveal the tectonic rejuvenation of the relief on the northern edge of the Guadalquivir basin, justifying this rejuvenation by the possible seismic activity of this fault [22]. In fact, the strong earthquakes (≥IX MSK) that occurred in the zone (Appendix A) have been linked to the backbulge collapse (normal faulting) of the isostatic forebulge of the Betic cordillera in the area [17,18,21,22]. As illustrated in Figure 2, the studied archaeological site is just located upon this complex flexural boundary, historically addressed as the "Guadalquivir Fault".…”

“…However, recent data on the flexural processes along the contact between the Paleozoic substratum of Sierra Morena and the Cenozoic Guadalquivir basin strongly suggest that they must be responsible of the recent seismicity along this important crustal boundary [17,18,25]. In addition, recent geomorphological studies reveal the tectonic rejuvenation of the relief on the northern edge of the Guadalquivir basin, justifying this rejuvenation by the possible seismic activity of this fault [22]. In fact, the strong earthquakes (≥IX MSK) that occurred in the zone (Appendix A) have been linked to the backbulge collapse (normal faulting) of the isostatic forebulge of the Betic cordillera in the area [17,18,21,22].…”

“…Nowadays, isolated patches of these eroded and uplifted Miocene materials lying unconformably on the metamorphic substratum provide evidence of the process (Figure 2B). Tectonic relief rejuvenation processes of the northern edge of the Guadalquivir basin have been described using geomorphological indexes and associated with the seismic activity of this fault [19][20][21][22]. As illustrated in Figure 1, NNE-SSW to nearly N-S normal faults segment the trace of the NE-SW border of the Guadalquivir Basin, a complex erosive-mechanical contact historically known as the "Great Betic Fault" or the Guadalquivir Fault Zone (GFZ) [21,22].…”

“…Tectonic relief rejuvenation processes of the northern edge of the Guadalquivir basin have been described using geomorphological indexes and associated with the seismic activity of this fault [19][20][21][22]. As illustrated in Figure 1, NNE-SSW to nearly N-S normal faults segment the trace of the NE-SW border of the Guadalquivir Basin, a complex erosive-mechanical contact historically known as the "Great Betic Fault" or the Guadalquivir Fault Zone (GFZ) [21,22]. The GFZ is a large fault-flexure fragmented (split) in multiple subparallel inducing the bending and upfolding of the Paleozoic basement for about 1500 m beneath the central sector of the basin to the northern reliefs of Sierra Morena [23].…”

“…[17,24]. This accumulated uplift will indicate uplift rates of about 0.09-0.1 mm/year, sufficient to explain the seismicity of the zone [17,22]. Crustal bending promoted and assisted brittle deformation at upper crustal levels (<30 km) resulting in NNE-SSW to NE-SW normal faulting in the backbulge zone [18,25] delineating the northern border of the basin (Figure 2).…”