Complete rupture of the Padul Fault represents one of the largest plausible earthquakes in the Sierra Nevada Range, one of the most seismically active regions of Spain. We performed a regional ...assessment of earthquake-triggered slope instabilities in the western part of the range to determine the most likely types of failures from such an earthquake in the region and suggest where such failures have a higher likelihood of occurring. These results are broadly useful for management of regional life-lines and future development. First, a slope-instability inventory of the Sierra Nevada was produced to identify the most common instability types. Subsequently, the Newmark’s sliding rigid-block methodology, implemented in a geographic information system, was used to obtain the distribution of Newmark displacements in the area considering a M w 6.6 earthquake on the Padul Fault. The Newmark displacements were then compared to the distribution of the inventoried slope instabilities to identify the areas where seismicity could reactivate old slope instabilities or generate new ones, and to identify the involved landslide typology. The most likely seismically induced slope instabilities in the Sierra Nevada are rock falls and rock slides. These types of instabilities could be triggered by Newmark displacements of 2 cm or less.
In this study, an inventory of landslides induced by the 2011 Lorca earthquake (Mw 5.1) has been used in order to develop a new procedure to obtain objective logic-tree weights for a probabilistic ...earthquake-induced landslide hazard analysis. The 2011 Lorca earthquake triggered more than 250 landslides, mainly of disrupted type. The logic-tree was designed having regard to variability of relevant geotechnical parameters involved in the problem and uncertainties associated with the use of several empirical relationships in order to compute Newmark displacements. For the purpose, the resulting hazard maps were compared with this landslide inventory, and weights estimated for each branch of the logic tree based on these results. The best model for seismic landslide hazard mapping for a moderate earthquake correctly identifies around 72% of landslide areas. Based on the set of parameters that comprises (depth of failure surface, specific weight, cohesion, friction angle and Newmark displacement model), the corresponding weights were objectively established. These weights are reliable enough for the obtaining seismic landslide hazard maps and may be implemented in similar environments characterized by moderate-low magnitude earthquakes (Mw < 5.5).
•A new method to obtain unbiased logic-tree weights in a probabilistic earthquake-induced landslide hazard analysis.•Influence of different variables and uncertainties in the resulting earthquake-induced landslide hazard maps.•An improvement of the well-known Newmark method is proposed.•The obtained weights can be applied to seismic landslide hazard maps assessments in low to moderate magnitude seismic areas.
Original volcanic edifices of two successive stages of Gran Canaria are reconstructed using a geomorphometric analysis of existent or restored paleosurfaces. In the reconstruction, surface fitting ...was applied preferably to planèzes (i.e. triangular facets of original volcano flanks) and quasi-planar surfaces, QPS (those occurring on planèzes, or scattered, slightly eroded portions derived from original cone surfaces) with the help of red relief image map (RRIM) analysis. Out of the long-lasting, Mid-Miocene to Holocene subaerial evolution of the island, the Late Miocene Fataga volcano and the subsequent, Pliocene Roque Nublo volcanoes were the largest and highest. The eruptive center of Fataga, a composite edifice (12.2–8.8Ma) that may have grown up excentrically with respect to the previous Tejeda caldera, is well-defined by both two planèzes (named Veneguera–Mogán and Fataga–Tirajana) and QPS remnants. Its calculated original volume, ≤1000km3, is close to the largest stratovolcanoes on Earth. However, its ≥3300m elevation, obtained by exponential fit, may have been significantly lower due to the complex architecture of the summit region, e.g. a caldera responsible for ignimbrite eruptions. Roque Nublo, a 3.7–2.9Ma stratovolcanic cone, which was superimposed upon the Fataga rocks ≥3km west of the Fataga center, has left no considerable paleosurfaces behind due to heavy postvolcanic erosion. Yet, its remnant formations preserved in a radial pattern unambiguously define its center. Moreover, surface fitting of the outcropping rocks can be corrected taking the erosion rate for the past 3Ma into account. Such a corrected surface fit points to a regular-shaped, ≥3000m-high cone with a 25km radius and ca. 940km3 original volume, also comparable with the dimensions of the largest terrestrial stratovolcanoes.
•Miocene–Pliocene volcanic edifices of Gran Canaria can be reconstructed by morphometry.•Paleosurfaces (planèzes and quasi planar surfaces) are a useful tool in reconstruction.•Fataga and Roque Nublo volcanoes had at least 900km3 original volume each.
This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western ...Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200
Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25
Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300
km in the north-western limb of the Western Moroccan Meseta.
In this work, a method for the fast evaluation of seismically-induced landslides is applied at regional scale in the Granada Basin (southern Spain). The methodology is based on the concept of rigid ...block but takes into account the variability in input data (geotechnical properties, failure depth and saturation state of the materials) through the use of a logical tree scheme. Input data were combined and evaluated using five different Newmark displacement empirical relations, which are automatically weighted to obtain a final co-seismic landslide susceptibility map. A Geographic Information System system was used to obtain the resulting maps considering the different branches and weights of the logic tree through an specifically developed automatic code written in Phyton. The landslides induced by the 2021 Mw 4.4 events of the Santa Fe seismic series have been used to validate the methodology. This is later used as input along with the road network to analyze the distribution of areas of different susceptibility level. The results obtained show that 1.73% of the total area is characterized by moderate to high susceptibility, being the southern and eastern sections of the Granada basin were more vulnerable slopes are found. When considering only zones around the road network (50 m buffer), it is found that 2.11% of slopes around highways and 1.33% of road slopes have moderate to high susceptibility, especially the A-92 highway and the A-338 road. These roads traverse areas with steep slopes and a combination of hard and soft materials, which increases the susceptibility of disrupted landslides. On the other hand, in more densely populated areas such as the metropolitan area of Granada, the susceptibility is lower due to their location on terrain with low to negligible slopes. The results are of interest for authorities managing slope stabilities because they allow establishing effective and locally-based seismic forecast works in order to minimize the damage of future events.
Abstract
In Arteara (Canary Island), a Holocene rock avalanche comprises accumulation of large reddish blocks which cover the Fataga ravine. This course, is entrenched into the Phonolitic Formation, ...an alternating sequence of lava flows and ignimbrites. The avalanche defines an elongated deposit of variable thickness. A low friction angle was deduced, which is related to an easily weathered bedrock favorable to the rolling of the blocks. The movement would have been a dry granular flow with a component of saltation at the head and of turbulent flow at the intermediate and distal areas. The deposit varies widely in size and is structured in bands of blocks with a polymodal distribution and low selection. The geomechanical properties of the rocks involved vary substantially in each block and along a longitudinal profile of the deposit. Schmidt Hammer rebound measured in 233 blocks show a polymodal dispersion. Some facies have been differentiated in the blocks, not only by their appearance, but also by their rebound index (R). The different hardness reflects the differences in density and porosity. The hardness zoning shows the differential weathering of the blocks, which depends on the rock anisotropy and the flow turbulence, which determines the influence of abrasion and punching of the blocks. The rebound shows a direct correlation with the bulk density and an inverse correlation with the distance to the source area.
•Fluvial drainage networks are sensitive to regional uplift.•Topographic changes in the eastern Rif massif are the result of active tectonics.•The drainage networks are locally strongly deformed in ...the studied region.•Uplift estimation shows that the E–W doming occurs during the Placenzian to Present.
This work studies the influence of active tectonics in the drainage networks and topography of the eastern Rif belt, eastern Middle Atlas, and Rekkame high plateau. We have performed a trend-topographic surface analysis at small to medium scales, several landscape analyses at medium scale, and the slope analysis of the relief. Furthermore, we have determined several geomorphic indices in the drainage networks of the study area: hypsometric curve analysis and normalised stream-length gradient (SLk) estimations. The trend-topography surface analysis identifies a NE–SW trending undulation that correspond to the positive topography of the Middle and High Atlas mountain ranges and the Rekkame high plateau as well as an E–W elongated dome in the eastern Rif-Beni Snassen massif. The geomorphologic indices indicate that drainage network is strongly deformed in the vicinity of the Trougout-Nekor active fault system. Furthermore, the Oued Molouya catchment is deformed in the northern limit of the Beni Snassen massif by active deformations accommodating a roughly N–S shortening. According to the available geochronological data from volcanic rocks as well as from Neogene to Quaternary sediments, the most likely age for the deformation of the drainage network producing the anomalous high geomorphic indexes was Placenzian to Present.
Interpretations of cavity expansion tests (pressuremeter, radial jack, etc.) are based (in most occasions) on the analysis of the deformability of a cylindrical cavity in a continuous, isotropic, and ...homogeneous medium. However, many rock masses show an anisotropic behaviour due to the presence of discontinuity planes of different origins. Cavity expansion tests in these media have been studied here with an empirical approach. Several tests have been simulated in a three-dimensional, anisotropic and discontinuous medium—using 3DEC by Itasca—and their deformation has been analyzed in order to establish the principal factors that control the behaviour of the rock mass in these situations. Based on this analysis, it has been developed a new method for the interpretation of the cavity expansion tests carried out in laminated rock masses, which allows estimating the principal deformation moduli of the rock mass (maximum and minimum). This method can be used for any dip of the discontinuity planes.
The Ossa de Montiel (2015/02/23, Mw4.7) earthquake struck the central part of Spain and was felt far from the epicenter (>300km). Even though ground shaking was slight (Imax=V, EMS-98 scale), the ...earthquake triggered many small rock falls, most at distances of 20–30km from the epicenter, greater than previously recorded in S Spain (16km) for earthquakes of similar magnitudes. The comparative analysis of available data for this event with records from other quakes of the Betic cordillera (S and SE Spain) seems to indicate a slower pattern of ground-motion attenuation in central Spain. This could explain why slope instabilities occurred at larger distances. Instability was more frequent, and occurred at larger distances, in road cuts than in natural slopes, implying that such slope types are highly susceptible to seismically induced landslides.
•A low magnitude earthquake induced rock falls at large distances from epicenter.•Maximum distances are greater than predicted by models according to event magnitude.•Ground motion attenuated slower than in areas tectonically active of SE Spain.•Instabilities were more frequent, and occurred at larger distances, in road cuts.
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