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Source models of mid-oceanic earthquakes are often based only on far-field, teleseismic data. The uncertainties of all source parameters are rarely quantified, which restricts our understanding of how these events slip and how oceanic lithosphere is formed. Here, we perform moment tensor inversions for five M w 4.6–5.9 earthquakes that occurred in the Azores archipelago near the Mid-Atlantic Ridge in 2013–2016, taking advantage of the recently expanded seismic network in the region. We assess moment tensor uncertainties due to data and Earth model variability as well as the robustness of teleseismic versus local data inversions. We find that for the events studied: (i) existing 1-D Earth models of the region based on receiver function data lead to a slightly improved data fit of local data compared to a widely used regional model based on active seismic surveys; and (ii) using different 1-D Earth models in the local data inversions leads to a variability in the retrieved source parameters of 15°–30° in fault strike, 5°–20° in dip, and 20°–60° in rake, depending on the earthquake's magnitude and location. We study in detail the M w 5.9 2013 April 30 Povoação basin earthquake using 1-D and 3-D waveform modelling, for which reported values of strike, dip, and rake in earthquake catalogues differ by 60°, 35°, and 80°. We find that our moment tensor solutions show a lower variability than in the catalogues and exhibit a persistent non-double-couple component of ∼40–60  per cent, which is not due to a volumetric change. We suggest that it is potentially due to geometrically complex faulting in the Povoação basin, notably curved faults. We find that the retrieved moment tensor solutions depend strongly on the earthquake's location. If an accurate location is used, joint inversions of local and teleseismic data can help to stabilize moment tensor solutions of oceanic earthquakes and reduce parameter trade-offs, compared to inversions of local data alone. [ABSTRACT FROM AUTHOR]

Strong ground motion prediction based on finite-fault simulation requires the identification of the fault (strike, dip, length and width), source kinematics parameters (stress drop, rupture velocity and slip distribution), regional crustal properties (geometrical spreading, anelastic structure, and upper crustal amplification and attenuation parameters) and the determination of amplification effects due to the local site geology. The general purpose of this study is to understand source and attenuation properties in the Azores, by the determination of stress drop, quality factor and kappa, through records obtained by the Portuguese digital seismic and accelerometer network. Source Spectra were obtained, for each record, after correcting observed spectra from geometrical spreading and anelastic attenuation effect: quality factor was estimated based on coda decay in the time domain and the kappa parameter was estimated by fitting the high-frequency decay of the acceleration spectrum with a straight line in a log-linear scale. Mean stress drop value was obtained considering that ω-squared model for the source spectra prevails. Parameters kappa, k, and quality factor, Q, have been estimated to be k = (0.075 ± 0.02)s and $$Q(f) = (76 \pm 11)f^{0.69 \pm 0.09}$$ , respectively. A mean value of stress drop was estimated to be around 90-130 bars for the earthquakes in analysis. The knowledge of source and path parameters, in association with other ground motion parameters, allows improving ground-motion estimates for the Azores and, consequently, will lead to more accurate seismic hazard assessment for the Azores and better characterization of seismic scenarios. [ABSTRACT FROM AUTHOR]

Marine predators may undergo remarkable dietary changes through time as a result of both anthropogenic and natural changes in the environment, but this variability is often difficult to tackle and seldom incorporated into ecosystem models. This paper uses the stable isotope ratios of carbon and nitrogen in skeletal material of South American sea lions from Brazilian scientific collections to investigate whether these animals modified their diet from 1986 to 2009, as reported for other marine predators in the region. Stable isotope ratios indicated that demersal potential prey were always enriched in C as compared with pelagic prey. Accordingly, the absence of any statistically significant correlation between stranding year and the δC values of adult males indicated no major increase in the consumption of pelagic prey from 1986 to 2009. Likewise, the results of the mixing model SIAR revealed a mixed diet including pelagic and demersal prey, with a central role for demersal fishes throughout the whole period. Furthermore, SIAR suggested no major changes in the proportion of pelagic and demersal prey in the diet of adult male South American sea lions during the past three decades. Demersal fishes were also relevant prey for juvenile South American sea lions during the whole period, but they always consumed a larger proportion of pelagic prey than the adults did. These results suggest no major changes in the diet of male South American sea lions during the past three decades in southern Brazil, contrary to what has been reported for other to predators in the regions and for the species in northern Patagonia. [ABSTRACT FROM AUTHOR]

In diving seabirds, sexual dimorphism in size often results in sex-related differences of foraging patterns. Previous research on Magellanic penguins, conducted during the breeding season, failed to reveal consistent differences between the sexes on foraging behavior, despite sexual dimorphism. In this paper, we tested the hypothesis that male and female Magellanic penguins differ in diet and foraging patterns during the non-breeding period when the constraints imposed by chick rearing activities vanish. We used stable isotope ratios of carbon and nitrogen in feather and bone to characterize the diet and foraging patterns of male and female penguins in the South Atlantic at the beginning of the 2009-2010 and 2010-2011 post-breeding seasons (feathers) and over several consecutive breeding and migratory seasons (bone). The mean δC and δN values of feathers showed no differences between the sexes in any of the three regions considered or in the diet composition between the sexes from identical breeding regions; however, Bayesian ellipses showed a higher isotopic niche width in males at the beginning of the post-breeding season. Stable isotope ratios in bone revealed the enrichment of males with δC compared with females across the three regions considered. Furthermore, the Bayesian ellipses were larger for males and encompassed those of females in two of the three regions analyzed. These results suggest a differential use of winter resources between the sexes, with males typically showing a larger diversity of foraging/migratory strategies. The results also show that dietary differences between male and female Magellanic penguins may occur once the constraints imposed by chick rearing activities cease at the beginning of the post-breeding season. [ABSTRACT FROM AUTHOR]

Data gathered by electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) were used to produce a three-dimensional image of subsurface soft-sediment deformation structures developed on the modern Lake Powell delta at Hite, Utah. ERT and GPR lines were run orthogonal across the crater. ERT resolved a low-resistivity layer up to 2 m thick in the area near the vents within the crater. This low-resistivity layer thins toward the margins representing clays ejected from the vents. Below and adjacent to this layer is a high-resistivity layer that reflects delta top and pro-delta sands. The deepest zone recognized in the ERT profiles consists of a low-resistivity layer, clay deposits that accumulated during the maximum lake high stand. This clay zone is connected to the vent within the crater by a conduit that changes diameter vertically. GPR profiles recognized the presence of collapse features restricted to the proximity of the vent. The geometry of the model is consistent with those proposed for marine pockmarks that can be generated seismically or aseismically with the exception of subaerial exposure after the dome stage development. [ABSTRACT FROM AUTHOR]