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One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M

The aim of this work is to make a synthesis at regional scale focused on the geophysical characterization of submarine faults around the Iberian margin to identify active structures and analyze their development in the framework of the present plate organization. Most of these submarine faults show seabed morphological expressions mapped with high-resolution swath bathymetry data, high-resolution parametric sub-bottom profiles and multichannel seismic profiles. Present active tectonics, deformation, seismicity, and tsunami-affected coastal areas is mainly focused on south Iberia at the Eurasian and Nubia plate boundary. Submarine active faults in these areas are represented by long strike-slip fault systems and arcuate fold-thrust systems. Their development takes place in response to present NW-SE convergence between the Eurasian and Nubia plates. We propose a strain partitioning model of the plate boundary into simple and pure shear zones to explain the distribution and mechanisms of active submarine faults along the Gulf of Cádiz, Gibraltar Arc and Alborán Sea in response to the present-day shear stress orientation. Nevertheless, deformation is also focused in the NW Iberian margin. Thus, along the Galician and Portuguese margin, several submarine faults mapped as thrust fault systems with high-seismic activity along the Iberian ocean-continent transition reflect the re-activation of former structures. We suggest that submarine active faults in the NW and W Iberia are also the response to the eastwards transfer of short-offset transform faults of the Mid Atlantic Ridge into the oceanic Iberian along a weakness as the former plate boundary between the oceanic Iberia and Eurasia domains. The distribution and activity of submarine faults mapped in this work from geophysical and bathymetric data are in good agreement with geodetic data and focal mechanisms. Versión del editor

One of the concerns of underground CO2 onshore storage is the triggering of Induced Seismicity and fault reactivation. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to the underground CO2 storage, based on the calculation of the strain field and defined by the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening respectively). This methodology is based on statistical analysis of individual strain tensor solutions obtained from fresh outcrops. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets role for underground fluid circulation can also be established, helping for further analysis about CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (Central Spain). The geology of the area and the number of high-quality outcrops, made this site as a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with the maximum horizontal shortening with N160° E and N50º E trend for local regime, which activates NE–SW strike-slip faults and NE–SW compressional faults. A regional tectonic field was also recognized with N–S trend, which activates E–W compressional faults. Monitoring of E–W faults within the reservoir is suggested in addition with the possibility of obtaining focal mechanism solutions for micro earthquakes (M

19 pages, 7 figures, The Alpine orogeny is well recorded onshore and offshore by tectonic inversion of the Mesozoic rift basins. Large scale linear seamounts (more than 250 km long and with up to 5 km of uplift) involving oceanic and continental lithosphere were carried on top of thrusts, such as the Gorringe seamount and the Estremadura Spur in the SouthWest and West Iberia Margin, respectively. The SouthWest Iberia Margin also recorded the westward migration of the Gibraltar Oceanic slab as the westwards propagation of the Neo-Tethys subduction. Rotation of the tectonic compression from NW-SE to WNW-ESE in Pliocene times caused the development of large scale dextral wrench faults as the present day Africa-Iberia plate boundary. Neotectonics of this plate boundary caused large to mega-scale destructive earthquakes and tsunamis

The Algarve Basin is a Meso-Cenozoic sedimentary basin overlying Carboniferous basement, located in the southwestern margin of the Iberian Peninsula. Its structure reveals a protracted tectonic history comprising various pulses of Mesozoic extension followed by Cenozoic compression. This work deals with the structure along the northern margin, where the Mesozoic extensional structures and Cenozoic inversion structures crop out. The strike of the extensional structures ranges from E–W to N–S, as controlled by a shift from Tethyan-dominated extension in the east to Atlantic-dominated extension in the west. Contractional structures are inverted extensional structures, following their same trends. It is argued that the thickness of the Hettangian evaporite layer exerts a strong control on the structural style throughout the basin during the extensional and inversion episodes. The basin is affected by thick-skinned deformation along the northern margin, where salt is thin or absent, basement involved fault systems and short-cut structures. Basinward, as the Hettangian salt thickens, the margin is affected by thin-skinned deformation, with listric and down-to-the-basin growth faults, diapirism and salt-cored detachment folds. The aim was to discuss the key tectonic features, the relevance of salt, and understand the nature, timing, and significance of all these structures in the regional tectonic evolution.

The southern Portuguese margin recorded significant extension and subsidence during the Jurassic, resulting in the formation of the Algarve basin. Recent studies have revealed the existence of oceanic crust, of potentially Jurassic age, underlying significant portions of the Gulf of Cadiz to the south and west of the Algarve basin, but the exact relationship between this basin and the oceanic crust is still ambiguous. In this study we integrate data derived from field outcrop studies, interpretation of commercial seismic, and gravity and magnetic modelling to better understand the transition from the rifted continental crust underlying the Algarve basin to the oceanic crust of the Gulf of Cadiz. This integrated approach reveals that the Gulf of Cadiz oceanic crust is related to the WSW-ENE trending Jurassic passive margin of southern Portugal, and is separated from the Algarve Basin by a domain of highly thinned continental crust.