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This work investigates the influence of rheological contrasts on the nucleation and behavior of strike-slip faults. To achieve this, we have carried out a series of brittle-viscous strike-slip shear analogue models, using quartz sand and microbeads as granular materials with different internal friction and cohesion values. Particle Imaging Velocimetry (PIV) was applied to time-series of surface images to calculate incremental and cumulative strains. Understanding how strike-slip faults nucleate and interact in the heterogeneous upper crust is relevant in seismic hazard analysis and geothermal and hydrocarbon exploration. To reproduce the heterogeneity of the upper crust, three sets of experiments we performed: 1) upper layer composed either of quartz sand or microbeads; 2) upper layer with a vertical contrast i.e., quartz sand surrounded by microbeads and vice-versa; and 3) same set-up as in the previous set but changing the orientation of the vertical contrast. Our study shows that the introduction of an upper crustal vertical contrast influences the behavior and evolution of strike-slip faults. The models containing a vertical contrast were more complex and induced a compartmentalization of the model. The initial fault strike is related to the material's properties. However, this initial strike changes when faults crosscut the materials with less internal friction angle clockwise, and anticlockwise when the contrast has higher internal friction angle. Areas containing materials with less internal friction angle take longer to localized the deformation, but they show a greater number of faults. The biggest increase in the number of synthetic and antithetic faults occurs with the introduction of vertical contrast. These results were compared with the intraplate fault systems of the NW Iberian Peninsula, focusing on the Penacova-Régua-Verin and Manteigas-Vilariça-Bragança fault systems. They are major left-lateral faults that cross-cut lithologies characterized by vertical rheological contrasts, with deformation patterns similar to those observed in our analogue models. [ABSTRACT FROM AUTHOR]

The Cabuérniga Fault System (CFS) extends for 150 km in E-W trend along the northern divide of the Cantabrian Mountains, near the Cantabrian Sea. This fault system was reactivated several times since the Paleozoic, and displays hydrothermal activity nowadays. We present here a detailed geological map of the whole CFS and six cross-sections distributed along strike, which allowed us to unravel the kinematic history of the individual fault segments comprising the CFS. The current CFS geometry mainly results from the reactivation of E-W Variscan thrusts and NW-SE Late-Variscan strike-slip faults during the Alpine Cycle. Reactivation took place in relation to both Permian and Mesozoic pre-orogenic extension and subsequent Cenozoic shortening. The eastern end of the CFS corresponds to a N-S structure arriving at the Cantabrian coast, while the western edge connects with the E-W trending Llanera fault, leading to an Alpine fault system extending 220 km. [ABSTRACT FROM AUTHOR]

Landslides are recognized as high-impact natural hazards in different regions around the world; therefore, they are extensively researched by experts. Landslide inventories are essential to identify areas that are likely to be affected in the future, thereby enabling interventions to prevent loss of life. Today, through combined approaches, such as remote sensing and machine learning techniques, it is possible to apply algorithms that use data derived from satellite images to produce landslide inventories. This work presents the performance of five machine learning methods—k-nearest neighbor (KNN), stochastic gradient descendent (SGD), support vector machine radial basis function (SVM RBF Kernel), support vector machine (SVM linear kernel), and AdaBoost—in landslide detection in a zone of the state of Guerrero in southern Mexico, using continuous change maps and primary landslide factors, such as slope angle, terrain orientation (aspect), and lithology, as inputs. The models were trained with 2/3 of ground truth samples of 671 slidden/non-slidden polygons. The obtained inventory maps were evaluated with the remaining 1/3 of ground truth samples by generating a confusion matrix and applying the Kappa concordance coefficient, accuracy, precision, recall, and F1 score as evaluation metrics, as well as omission and commission errors. According to the results, the AdaBoost classifier reached greater spatial and statistical coherence than the other implemented methods. The best input layer combination for detection was the continuous change maps obtained by the linear regression and image differencing detection methods, together with the slope angle, aspect, and lithology conditioning factors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lateritic clays occur in fault contact with granites in a Cenozoic basin. • Geochemical data indicates an allochthonous mafic source for the lateritic clays. • Hydrothermal fluids interacted with the lateritic clays and the granites. • Faults had extensional component and were re-activated with inverse strike-slip. • Faults were not effective seals for the hydrothermal fluids. Continental basin evolution can be influenced not only by tectonic activity, but by hydrothermal and weathering processes. This is displayed on the basement rocks (granites and xenoliths) and sedimentary cover (clays, sands and conglomerates) in the Cenozoic Ferreira basin of NW Spain. In this study, we applied petrological, geochemical and structural proxies to investigate a red clay unit and adjacent granitic basement rocks in a fault contact. Red clays have a lateritic composition (SiO 2 : 38–42 wt%, Fe 2 O 3 : 13–20 wt% and Al 2 O 3 : 24–29 wt%) with moderate to high contents in V (267 – 324 ppm) and Ni (46–71 ppm), and are characterized by (La/Yb) n and TREE that vary from ∼5 to 12 and ∼55 to 110 ppm, respectively. The basement rocks are peraluminous biotite granites (A/CNK: 1.12–13.57) with (La/Yb) n and TREE that vary from 7.7 to 27.42 and from 82.79 to 244.64 ppm, respectively. The xenoliths are peraluminous shales (A/CNK: 3.48–4.48) with (La/Yb) n and TREE varying from 7.66 to 11.10 and from 228.61 to 344.42 ppm, respectively. This geochemistry indicates that the lateritic red clays come from residual weathering of mafic ± intermediate rocks. They are interpreted to have been generated under the tropical climate conditions in the Late Cretaceous (∼70 Ma). Afterwards red clays were remobilized in subsequent tectonic events (Alpine), deposited in faulted grabens, and together with adjacent basement granites, affected by hydrothermal events that caused element mobility (e.g., REE leaching and Ce positive anomalies). Fault reactivations, under strike-slip stresses with a reverse component, channelized these hydrothermal fluids and uplifted part of the landscape. This uplift is interpreted as the trigger of an erosional regime that affected the lateritic red clay unit in the Ferreira basin. The conclusions of this study highlights the important interplay of different geological processes in small continental basins. [ABSTRACT FROM AUTHOR]

The Hope fault is the most active and southernmost splay of the Marlborough fault system in the northern South Island of New Zealand. The fault consists of five geometrically defined segments. We used trenching to acquire paleoseismic data and radiocarbon dating of faulted late Holocene sediments on the Hurunui segment of the Hope fault to derive an earthquake chronology that extends from the historic 1888 Mw 7.1 Amuri earthquake to ca. 300 C.E., thereby providing the longest chronologic record of earthquakes on the Hope fault to date. Earthquake event horizons were identified by upward fault terminations, colluvial wedges, unconformities, and/or progressive folding of shutter basin deposits. Six earthquakes identified at C.E. 1888, 1740-1840, 1479-1623, 819-1092, 439-551, and 373-419 indicate a mean recurrence interval of ~298 ± 88 yr, with successive median interevent times ranging from 98 to 595 yr. The large variance in interevent times with respect to mean recurrence interval is explained by (1) possible coalescence of rupture overlap from the adjacent Hope River segment onto the Hurunui segment at our study site (including the 1888 Mw 7.1 Amuri earthquake, sourced primarily from the Hope River segment), which results in apparently shorter interevent times at the study site compared to mean recurrence intervals from adjacent fault segments, (2) possible earthquake temporal clustering on the Hurunui segment, which could result in interevent times that are significantly shorter or longer than interevent times and mean recurrence intervals predicted by a periodic earthquake rupture model, and/or (3) "missing" events, which could result in interevent times and mean recurrence intervals at the study site that are longer than the actual mean recurrence interval. While we cannot exclude option 3 as a possibility, we prefer options 1 and 2 to explain earthquake chronologies and rupture behavior on the Hurunui segment of the Hope fault, given the detailed nature of our geologic and chronologic investigations. By demonstrating that the 1888 Amuri earthquake propagated through a proposed segment boundary, we provide the first evidence for coseismic multisegment ruptures on the Hope fault. In contrast, the penultimate earthquake ruptured the Hurunui segment at 1740-1840 C.E. with no known rupture of the Hope River segment. Paleoearthquake records near geometrically complex segment structural boundaries on major strike-slip faults may show temporal recurrence distributions resulting from earthquake ruptures that variably arrest or propagate through proposed segment boundaries. We note that earthquake recurrence along major strikeslip plate-boundary faults may vary between more periodic and more episodic end members, even on adjacent, geometrically defined segments. [ABSTRACT FROM AUTHOR]