Examinando por Autor "Alfaro, Pedro"
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Ítem 3D geometry and architecture of a normal fault zone in poorly lithified sediments: A trench study on a strand of the Baza Fault, central Betic Cordillera, south Spain.(Elsevier, 2019) Medina-Cascales, Iván; Koch, Leah; Cardozo, Néstor; Alfaro, Pedro; García-Tortosa, Francisco JuanSuccessive excavation of 13 trenches of different orientations reveals the complexity of a normal fault zone in Pliocene-Pleistocene unconsolidated sediments on a strand of the Baza Fault, central Betic Cordillera, south Spain. These trenches and the excavation floor are interpreted and integrated to reconstruct the 3D geometry and internal architecture of the fault zone. The structure consists of two main fault strands: an eastern one with a few hundred metres throw and a western one with at least 15m throw. These strands interact and gradually merge to the south, bounding a main deformation zone narrowing from ∼7 to 1m along strike. Fault-bounded rock bodies, clay and sand smears, and clay injections define the structure. These features are highly variable in 3D. In the northern part of the outcrop, deformation is localized around the main strands, brittle in the west and more ductile to the east. As the strands and their fault zones increasingly interact, fault throw, rock deformation and maturity of the structure increase. Mechanical stratigraphy also controls the style of deformation. A realistic representation of this 4D picture of fault deformation is critical for modelling fluid flow in shallow to possibly deep, faulted sedimentary reservoirs.Ítem Active faulting in the central Betic Cordillera (Spain): Palaeoseismological constraint of the surface-rupturing history of the Baza Fault (Central Betic Cordillera, Iberian Peninsula).(Elsevier, 2018) Castro-Sabio, Julia; Martín-Rojas, Iván; Medina-Cascales, Iván; García-Tortosa, Francisco Juan; Alfaro, Pedro; Insua-Arévalo, Juan MiguelThis paper on the Baza Fault provides the first palaeoseismic data from trenches in the central sector of the Betic Cordillera (S Spain), one of the most tectonically active areas of the Iberian Peninsula. With the palaeoseismological data we constructed time-stratigraphic OxCal models that yield probability density functions (PDFs) of individual palaeoseismic event timing. We analysed PDF overlap to quantitatively correlate the walls and site events into a single earthquake chronology. We assembled a surface-rupturing history of the Baza Fault for the last ca. 45,000 years. We postulated six alternative surface rupturing histories including 8–9 fault-wide earthquakes. We calculated fault-wide earthquake recurrence intervals using Monte Carlo. This analysis yielded a 4750–5150 yr recurrence interval. Finally, compared our results with the results from empirical relationships. Our results will provide a basis for future analyses of more of other active normal faults in this region. Moreover, our results will be essential for improving earthquake-probability assessments in Spain, where palaeoseismic data are scarce.Ítem How Much Nubia‐Eurasia Convergence Is Accommodated by the NE End of the Eastern Betic Shear Zone (SE Spain)? Constraints From GPS Velocities(American Geophysical Union, 2019-04-29) Borque, María Jesús; Sánchez-Alzola, Alberto; Martín-Rojas, Iván; Alfaro, Pedro; Molina-Palacios, Sergio; Rosa-Cintas, Sergio; Rodríguez-Caderot, Gracia; de Lacy, María Clara; García-Armenteros, Juan Antonio; Avilés-Moreno, Manuel; Herrera-Olmo, Antonio Manuel; García-Tortosa, Francisco Juan; Estévez-Rubio, Antonio; Gil-Cruz, Antonio JoséWe present the first GPS-derived geodetic observations from the NE end of the Eastern Betic Shear Zone obtained from the Bajo Segura GPS network (SE Spain). The network has 11 GPS sites and was sampled four times between 1999 and 2013. Despite the low signal-to-noise ratio of the residual velocities obtained, the velocities are nonzero at 95% confidence level. We postulate that the GPS data point to the partitioning of deformation into the NNW–SSE shortening and a N70E left-lateral component. The maximum deformation rates are located along the two main active faults in the study area. The maximum shortening rates (north component) in the southern region of the Bajo Segura Basin vary from west to east, ranging from 0.2 to 0.7 mm/year along the Bajo Segura Fault Zone. On the northern border of the basin, along the Crevillente Fault Zone, left-lateral displacement varies between 0.4 and 0.7 mm/year in the E-W direction. The GPS-based regional geodynamic models of the Western Mediterranean indicate that the residual shortening of the Eurasia-Nubia plate convergence is accommodated in the eastern part of the Iberian Peninsula and the Algero-Balearic Basin. Our results indicate that part of this residual deformation occurs at the NE end of the Eastern Betic Shear Zone, but significant deformation must be accommodated also to the north (External Betics) and to the south (Cartagena Basin and offshore area). We postulate that Eurasia-Nubia plate convergence is transferred to the Eastern Betics because of the thin and rigid (potentially oceanic) crust of the Algero-Balearic Basin, which acts as an indenter.Ítem Insights of Active Extension Within a Collisional Orogen From GNSS (Central Betic Cordillera, S Spain)(Whiley, 2023-06-13) Martín-Rojas, Iván; Alfaro, Pedro; Galindo, Jesús; Borque, María Jesús; García-Tortosa, Francisco Juan; Sanz-de Galdeano, Carlos; Avilés-Moreno, Manuel; Sánchez-Alzola, Alberto; González-Castillo, Lourdes; Ruano, Patricia; Medina-Cascales, Iván; Tendero-Salmerón, Víctor; Madarieta-Txurruka, Asier; Pedrosa-González, María Teresa; Gil-Cruz, Antonio JoséThe coexistence of shortening and extensional tectonic regimes is a common feature in orogenic belts. The westernmost end of the Western Mediterranean is an area undergoing shortening related to the 5 mm/yr NNW‒SSE convergence of the Nubia and Eurasia Plates. In this region, the Central Betic Cordillera shows a regional ENE‒WSW extension. Here, we present GNSS-derived geodetic data along a 170 km-long transect orthogonal to the main active normal faults of the Central Betic Cordillera. Our data indicate that the total extension rate along the Central Betic Cordillera is 2.0 ± 0.3 mm/yr. Extension is accommodated in the eastern (0.8 ± 0.3 mm/yr in the Guadix-Baza Basin) and western (1.3 ± 0.3 mm/yr in the Granada Basin) parts of the Central Betic Cordillera, while no extension is recorded in the central part of the study area. Moreover, our data permit us to quantify, for the first time, short-term fault slip rates of the Granada Fault System, which is one of the main seismogenic sources of the Iberian Peninsula. We deduce a fault slip rate of ∼1.3 ± 0.3 mm/yr for the whole Granada Basin, with 0.9 ± 0.3 mm/yr being accommodated in the Granada Fault System and 0.4 ± 0.3 mm/yr being accommodated in the southwestern sector of the Granada Basin, where no active faults have been previously described at the surface. The heterogeneous extension in the Central Betic Cordillera could be accommodated by shallow high-angle normal faults that merge with a detachment at depth. Part of the active extension could be derived from gravitational instability because of underlying over-thickened crust.Ítem Tectonic geomorphology of an active slow-moving, intrabasinal fault: the Galera Fault (Guadix-Baza Basin, central Betic Cordillera, southern Spain)(Elsevier, 2021) Medina-Cascales, Iván; García-Tortosa, Francisco Juan; Martín-Rojas, Iván; Pérez-Peña, Vicente; Alfaro, PedroIn this work, we prove the usefulness of morphometric analyses, typically applied to basin-border faults, to define the tectonic geomorphology of a slow-moving, intrabasinal structure: the Galera Fault (Guadix-Baza Basin, southern Spain). The Galera Fault is a 30 km-long, oblique-slip fault with major left-lateral and minor vertical slip components. Through geological and structural analyses, we define for the first time the detailed surface geometry of the fault, which is characterized by features typical of left-lateral strike-slip faults. The morphometric analysis indicates that a combination of slow slip rates and the high erodibility of the juxtaposed basin infill deposits favours a rapid landscape response to fault activity that erases many landscape effects related to active tectonics. This masking is more effective on features generated by strike-slip displacement, leaving only subtle evidence, such as local stream deflections and upstream widening of catchments. In contrast, geomorphic effects related to vertical displacement are better preserved, including the control of the geometry of the main rivers and morphological differences in the drainage network between the two fault blocks. On the upthrown fault block, streams are generally shorter and steeper and have greater valley incision, leading to the development of a badland landscape. Moreover, the vertical deformation of a Middle Pleistocene glacis surface (ca. 90 m) demonstrates the important role of this slow-moving intrabasinal fault in the generation of relief in the Betic Cordillera during recent Quaternary time. Although the impact of this fault on relief building is very low in comparison with oblique-slip, basin-border faults in the mountain range, it has a key control on the Quaternary landscape evolution.Ítem The Campo de Dalias GNSS Network Unveils the Interaction between Roll-Back and Indentation Tectonics in the Gibraltar Arc(MDPI, 2022-03-09) Galindo, Jesús; Gil-Cruz, Antonio José; Tendero-Salmerón, Víctor; Borque, María Jesús; Ercilla, Gemma; González-Castillo, Lourdes; Sánchez-Alzola, Alberto; de Lacy, María Clara ; Estrada, Ferran; Avilés-Moreno, Manuel; Alfaro, Pedro; Madarieta-Txurruka, Asier; Chacón, FernandoThe Gibraltar Arc includes the Betic and Rif Cordilleras surrounding the Alboran Sea; it is formed at the northwest-southeast Eurasia–Nubia convergent plate boundary in the westernmost Mediterranean. Since 2006, the Campo de Dalias GNSS network has monitored active tectonic deformation of the most seismically active area on the north coast of the Alboran Sea. Our results show that the residual deformation rates with respect to Eurasia range from 1.7 to 3.0 mm/year; roughly homogenous west-southwestward displacements of the northern sites occur, while the southern sites evidence irregular displacements towards the west and northwest. This deformation pattern supports simultaneous east-northeast–west-southwest extension, accommodated by normal and oblique faults, and north-northwest-south-southeast shortening that develops east-northeast–west-southwest folds. Moreover, the GNSS results point to dextral creep of the main northwest–southeast Balanegra Fault. These GNNS results thus reveal, for the first time, the present-day interaction of the roll-back tectonics of the Rif–Gibraltar–Betic slab in the western part of the Gibraltar Arc with the indentation tectonics affecting the eastern and southern areas, providing new insights for improving tectonic models of arcuate orogens.