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Despite that earthquakes in stable continental regions (SCR) often cause more damage than interplate seismicity, they remain poorly understood. This is mainly because of the lower rate of intraplate seismicity and because of its different behaviour compared to the better-known seismicity at the plate boundary. Understand the characteristics of the intraplate seismicity is a challenge for the seismic risk studies. We study and characterise an SCR (NW Iberian Peninsula), which not only registers moderate instrumental intraplate seismicity, but also important historic seismicity and paleoseismic activity. To tackle some of the difficulties posed by intraplate seismicity, we analyse a wide and multidisciplinary data set (e.g., geological structures, seismicity, focal mechanisms, and geophysical data). Seismicity in this region is not associated with an old rift, but with inherited faults widely distributed throughout the region with a great variety of orientations. The reactivation kinematics of these faults are coherent with the current regional stresses. Instrumental seismicity is not associated with the large active faults nor with crustal limits. Seismicity is mainly clustered in swarms and sequences. Although seismic swarms present lower magnitudes, they are the most common. Based on swarms' characteristics (high b-values, upward spatiotemporal migration), reported mantellic CO2 in some thermal springs, and the reactivation of inherited steeply-dipping faults, we propose the migration of deep fluids through steeply-dipping fractured areas as the cause of the intraplate seismicity. These processes could increase the pore pressure and decrease the stresses necessary for the fault rupture in a fault-valve behaviour. In general, in intraplate context, the important control in the seismicity of the inherited fault systems favourable oriented under the current stress tensor is observed, and also the need for mechanisms that can decrease the effective stress for the fault ruptures. Mechanisms as hydrothermal fluids in arterial faults with fault-valve processes has been identified as an effective driver of intraplate seismicity, playing an important role in stability of tectonic faults. The large number and variety of these faults, that share the low strain rates in intraplate polyorogenic context, may explain the different characteristics of these intraplate regions compared with the interplate regions, as the "unanticipated" behaviour, variety of kinematics, the long quiescence periods without seismicity associated and erosion obliterating their morphotectonic expression. • Seismogenic faults are inherited fault systems reactivated under current stress field. • Intraplate characteristics due to the large number and variety of inherited faults. • Need for mechanisms that can decrease the effective stress for the fault ruptures. • Deep fluid migration in subvertical faults decrease effective stress. • Fluids migration in a fault-valve behaviour responsible for seismic swarms. [ABSTRACT FROM AUTHOR]

Abstract Rift zones are fundamental features in oceanic island volcanoes, although their origin is still controversial, especially at the Canary Islands where the role of volcanic spreading is under debate. For this reason, we have performed a field study of > 400 dykes at 20 outcrops in the Lower Old Edifice and 2 outcrops of the Upper Old edifice of La Gomera Island, identifying different dyke swarms. We propose the development of an unnoticed E-W volcanic rift (Hermigua Rift) restricted to the Lower Old Edifice East flank, with up to 25% of extension and structural characteristics compatible with the spreading of the edifice over a basal weak decollement. Contemporaneously a dyke swarm of outward-dipping dykes intruded at the W-SW zones, indicating a progressive radial sliding of the edifice. This asymmetric volcano structural pattern suggests that volcano stresses were predominately local in origin, probably related to the buttressing effect of the neighbor contemporaneous Roque del Conde edifice (Tenerife Island). Additionally, we have deduced two different rift zones (NW-SE Enchereda and N-S Erque rifts) during the growth of the Upper Old Edifice, evidencing that La Gomera rifts were dynamic evolving structures. The structure and regional setting of the Upper Old Edifice rifts suggest a change to a predominance of regional stresses. Our results have implications for the understanding of the origin and evolution of rifts at oceanic island volcanoes, since: 1) confirm a principal role for volcanic spreading processes; 2) support that the location of neighbor volcanic loads strongly influences rifts development; and 3) suggests, in some situations, a possible main role for the regional stress field. Highlights • We identify several unnoticed rift zones at Old Volcanic Edifice of La Gomera by their underlying coherent dike complexes. • An unnoticed E-W structure (Hermigua Rift) developed at the east flank of the Lower Old Edifice with up to 25% of extension. • Contemporaneously a singular swarm of outward dipping dikes developed at the volcano west flank. • Asymmetric volcano structural pattern suggests that volcano stresses were local in origin related to the volcano spreading. • The neighbour contemporaneous Roque del Conde edifice (Tenerife Island) produced a buttressing effect. • Two new rift zones (NW-SE Enchereda and N-S Erque rifts) developed during the growth of the Upper Old Edifice. • Rifts of the Old Volcanic Edifice of La Gomera were dynamic evolving structures. • The character of the Upper Old Edifice rifts suggest a change to a predominance of regional stresses during its growth. [ABSTRACT FROM AUTHOR]

Pleistocene fluvial incision acceleration resulting in narrow and deeply entrenched valleys has been widely described and is generally attributed to uplift rate increase or greater climatic severity. In this paper, the long-term downcutting pattern of the Upper Ebro River and driving mechanisms are assessed, and we reconstruct the valley incision recorded by an outstanding sequence of 22 river terraces. Dating of 8 fluvial levels by means of the ESR, TCN, and OSL techniques, spanning the last 1.2 Ma, reveals a long-term incision deceleration pattern. The estimated age-incision model indicates a decrease in the incision rates, showing a long-term deceleration during the final Early Pleistocene (from 0.42 to 0.18 m/ka), and a tendency towards a steady state or base level stabilization from the Middle Pleistocene (0.15–0.03 m/ka) to the Late Pleistocene (0.03 m/ka). This incision pattern does not support climate change as a long-term incision-acceleration driver by itself, demonstrating the need for base level lowering effects to have operated. Upper Ebro deceleration incision is explained by the headward attenuation of the incision wave induced by the opening of the Ebro Cenozoic Basin in a geodynamic context characterized by an absence of significant uplift over the last million years. This trend could have changed the aggressor-victim roles of the rivers involved in fluvial captures at the drainage divide. The documented incision deceleration pattern differs from that reported for other valleys in the Iberian Peninsula, suggesting that the degree of maturity of the fluvial systems depends on their relative position with respect to the capture point, in addition to tectonic and lithostructural factors. In the Late Pleistocene-Holocene, a short-lived incision rate increase is recorded, corresponding to the last terrace dissection phase, during the transition from the last glacial MIS 2 to the interglacial MIS 1. • Incision acceleration is widely reported during Pleistocene valley entrenchment. • However, the Upper Ebro valley contains a complex sequence of fluvial terraces • which were dated within the last 1.2 Ma using ESR, TCN and OSL techniques • and indicate an incision deceleration pattern. • This suggests that the river incision is tending to a steady state. [ABSTRACT FROM AUTHOR]

In the northern Iberian Peninsula, the Pyrenean-Cantabrian orogenic belt extends E-W for ca. 1000 km between the Atlantic Ocean and Mediterranean Sea. This orogen developed from the collision between Iberia and Eurasia, mainly in Cenozoic times. Lower-middle Permian sediments crop out in small, elongated basins traditionally considered independent from each other due to misinterpretations on incomplete lithostratigraphic data and scarce radiometric ages. Here, we integrate detailed stratigraphic, sedimentary, tectonic, paleosol and magmatic data from well-dated lithostratigraphic units. Our data reveal a similar geodynamic evolution across the Pyrenean-Cantabrian Ranges at the end of the Variscan cycle. Lower-middle Permian basins started their development under an extensional regime related to the end of the Variscan Belt collapse, which stars in late Carboniferous times in the Variscan hinterland. This orogenic collapse transitioned to Pangea breakup at the middle Permian times in the study region. Sedimentation occurred as three main tectono-sedimentary extensional phases. A first phase (Asselian-Sakmarian), which may have even started at the end of the Carboniferous (Gzhelian) in some sections, is mainly represented by alluvial sedimentation associated with calc-alkaline magmatism. A second stage (late Artinskian–early Kungurian), represented by alluvial, lacustrine and palustrine sediments with intercalations of calc-alkaline volcanic beds, shows a clear upward aridification trend probably related to the late Paleozoic icehouse-greenhouse transition. The third and final stage (Wordian-Capitanian) comprised of alluvial deposits with intercalations of alkaline and mafic beds, rarely deposited in the Cantabrian Mountains, and underwent significant pre- and Early Mesozoic erosion in some segments of the Pyrenees. This third stage can be related to a transition towards the Pangea Supercontinent breakup, not generalized until the Early/Middle Triassic at this latitude because the extensional process stopped about 10 Myr (Pyrenees) to 30 Myr (Cantabrian Mountains). When compared to other well-dated basins near the paleoequator, the tectono-sedimentary and climate evolution of lower-middle Permian basins in Western and Central Europe shows common features. Specifically, we identify coeval periods with magmatic activity, extensional tectonics, high subsidence rates and thick sedimentary record, as well as prolonged periods without sedimentation. This comparison also identifies some evolutionary differences between Permian basins that could be related to distinct locations in the hinterland or foreland of the Variscan orogen. Our data provide a better understanding of the major crustal re-equilibration and reorganization that took place near the equator in Western-Central Europe during the post-Variscan period. • The beginning of the Iberian Variscan orogenic collapse is late Carboniferous in the hinterland and early Permian towards the foreland. • Variscan orogenic collapse is associated with calc-alkaline magmatism that shifts to alkaline magmatism in middle Permian times. • The beginning of the Alpine cycle of sedimentation in the whole Pyrenean ranges occurred as three main Permian tectono-sedimentary extensional phases. • The Permian tectono-sedimentary evolution of the Pyrenean ranges shows common features to the ones of Central and W Europe basins. [ABSTRACT FROM AUTHOR]