Selection and ranking of ground motion models for seismic hazard analysis in the Pyrenees

The issue addressed in this paper is the objective selection of appropriate ground motion models for seismic hazard assessment in the Pyrenees. The method of Scherbaum et al. (2004a) is applied in order to rank eight published ground motion models relevant to intraplate or to low deformation rate contexts. This method is based on a transparent and data-driven process which quantifies the model fit and also measures how well the underlying model assumptions are met. The method is applied to 15 accelerometric records obtained in the Pyrenees for events of local magnitude between 4.8 and 5.1, corresponding to moment magnitudes ranging from 3.7 to 3.9. Only stations at rock sites are considered. A total of 720 spectral amplitudes are used to rank the selected ground motion models. Some control parameters of these models, such as magnitude and distance definitions, may vary from one model to the other. It is thus important to correct the selected models for their difference with respect to the magnitude and distance definitions used for the Pyrenean data. Our analysis shows that, with these corrections, some of the ground motion models successfully fit the data. These are the Lussou et al. (2001) and the Berge-Thierry et al. (2003) models. According to the selected ground motion models, a possible scenario of a magnitude 6 event is proposed; it predicts response spectra accelerations of 0.08–0.1 g at 1 Hz at a hypocentral distance of 10 km.     

Patterns and drivers of asteroid abundances and assemblages on the continental margin of Atlantic Canada

Although continental shelf and slope environments typically exhibit high epifaunal biomass and have been subjected to increasing fishing pressure, ecological information on assemblages of non‐commercial invertebrate species from subtidal and bathyal areas remains limited. Sea stars (Echinodermata: Asteroidea), which are known to influence communities through their feeding habits, have received less attention than structural taxa such as corals and sponges. To better understand the ecological roles of asteroids on continental shelves, we investigated ~30 species and assessed their distributions and co‐occurrence with other benthic invertebrates on the shelf and slope of Eastern Canada. Using fisheries data and in situ video footage, we compiled a large dataset covering ~600,000 km² that included over 350,000 individual asteroid records (37–2243 m depth). Multivariate analyses revealed geographically distinct asteroid assemblages, with a maximal overall density at 400–500 m and the highest diversity at 500–700 m. The most abundant and densely occurring species was Ctenodiscus crispatus. We found that asteroids associate with corals, sponges, bivalves, and other echinoderms, and that depth and substrate influence these assemblages. We identified species likely to affect coexisting organisms by their burrowing behavior that can disrupt epi‐ and infauna (C. crispatus) and through predation on ecologically important corals (Hippasteria phrygiana). In addition to providing baseline distribution and ecological information for many bathyal asteroid species in the Northwest Atlantic, this work highlights the abundance and diversified roles of asteroids within continental shelf and slope ecosystems.     

The impact of inter-flood duration on non-cohesive sediment bed stability

Limited field and flume data suggests that both uniform and graded beds appear to progressively stabilize when subjected to inter-flood flows as characterized by the absence of active bedload transport. Previous work has shown that the degree of bed stabilization scales with duration of inter-flood flow, however, the sensitivity of this response to bed surface grain size distribution has not been explored. This article presents the first detailed comparison of the dependence of graded bed stability on inter-flood flow duration. Sixty discrete experiments, including repetitions, were undertaken using three grain size distributions of identical D₅₀ (4.8 mm); near-uniform (σ_g = 1.13), unimodal (σ_g = 1.63) and bimodal (σ_g = 2.08). Each bed was conditioned for between 0 (benchmark) and 960 minutes by an antecedent shear stress below the entrainment threshold of the bed (τ*_c50). The degree of bed stabilization was determined by measuring changes to critical entrainment thresholds and bedload flux characteristics. Results show that (i) increasing inter-flood duration from 0 to 960 minutes increases the average threshold shear stress of the D₅₀ by up to 18%; (ii) bedload transport rates were reduced by up to 90% as inter-flood duration increased from 0 to 960 minutes; (iii) the rate of response to changes in inter-flood duration in both critical shear stress and bedload transport rate is non-linear and is inversely proportional to antecedent duration; (iv) there is a grade dependent response to changes in critical shear stress where the magnitude of response in uniform beds is up to twice that of the graded beds; and (v) there is a grade dependent response to changes in bedload transport rate where the bimodal bed is most responsive in terms of the magnitude of change. These advances underpin the development of more accurate predictions of both entrainment thresholds and bedload flux timing and magnitude, as well as having implications for the management of environmental flow design. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Analysis of hydrobiological pattern in the Bizerte lagoon (Tunisia)

This study deals with the use of a multivariate analysis method in order to understand the functioning of the Bizerte lagoon ecosystem. A set of hydrobiological parameters was collected during 10 monthly campaigns in 2004. A variant of the EOF (Empirical Orthogonal Function) technique is used to examine hydrobiological variability modes in this lagoon. The permanent features characterising the lagoon are obtained by applying the EOF technique to data after removing the annual cycle. Two major modes were obtained. The first one shows a contrast between the northern sector of the lagoon, influenced by the Mediterranean Sea, and the southern one influenced by continental waters. This mode is mostly prominent for temperature and salinity. The second mode shows a contrast between shallow waters along the coastal zones and the deep central area of the lagoon. This contrast is more pronounced towards the southwestern edge of the lagoon, a region of important freshwater input from the Tinja channel, which drifts towards the downstream area of Menzel Bourguiba. This second mode may also correspond to northward water circulation under southerly wind blowing frequently in summer. The spatial and temporal variability in the lagoon is highlighted by applying the EOF to the raw data without removing the annual cycle. A weight series is obtained for each variable by extracting the corresponding data and then projecting them on the corresponding eigenvector. Using this technique, only one mode was found dominant with more than 52% of the total variance. It was also found that the north–south contrast of temperature, salinity and phosphorous and the coast-centre contrast of Chlorophyll a are enhanced in summer. Other variables such as ammonia and nitrate also show significant annual cycles but with local patterns.     

Isotope and trace element geochemistry of Colorado Plateau volcanics

Basalts from the San Francisco Peaks and North Rim of Grand Canyon, nephelinites from the Hopi Buttes and Navajo minettes (Colorado Plateau) have been analyzed for trace element contents and Sr, Nd, Pb isotope compositions. The ages increase eastward from the Quaternary (basalt) to 5 Ma (nephelinite) and 30 Ma (minette) as does the depth of melt generation inferred from xenolith mineralogy and major element geochemistry.

The three rock types present an enrichment of incompatible elements (although minettes present negative concentration spikes for Nb, Zr, Ti, Ba, Sr) relative to other magma types. The chondrite-normalized Ce/Yb ratio changes from 8–22 (basalt) to 25–30 (nephelinite) and 33–60 (minette) and reflects small degrees of partial melting of a mantle source with a garnet/clinopyroxene ratio increasing with depth. The negative Eu anomaly present in minette, the low Sr/Nd and high Pb/Ce suggest the presence of a recycled continental crust component in their mantle source.

The ⁸⁷Sr/⁸⁶Sr ratio varies from 0.7032-0.7045 (basalt and nephelinite) to 0.7052-0.7071 (minette), while ε_Nd is remarkably more constant at +0.8 to +3.7 (nephelinite) and −2.6 to +2.2 (basalt and minette). Good linear correlations are observed in both ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagrams with basalt being the least and nephelinite the most radiogenic and indicate a 2.3 ±0.1 Ga age and a Th/U of 3.4.

Three lithospheric source components are indicated: a) an OIB-type depleted mantle source, b) an end-member with unradiogenic Sr, Nd and Pb for basalt and nephelinite and c) a recycled crustal component for minette.     

Community collaboration and climate change research in the Canadian Arctic

Research on climate change impacts, vulnerability and adaptation, particularly projects aiming to contribute to practical adaptation initiatives, requires active involvement and collaboration with community members and local, regional and national organizations that use this research for policy-making. Arctic communities are already experiencing and adapting to environmental and socio-cultural changes, and researchers have a practical and ethical responsibility to engage with communities that are the focus of the research. This paper draws on the experiences of researchers working with communities across the Canadian Arctic, together with the expertise of Inuit organizations, Northern research institutes and community partners, to outline key considerations for effectively engaging Arctic communities in collaborative research. These considerations include: initiating early and ongoing communication with communities, and regional and national contacts; involving communities in research design and development; facilitating opportunities for local employment; and disseminating research findings. Examples of each consideration are drawn from climate change research conducted with communities in the Canadian Arctic.     

CoRoT-2a Magnetic Activity: Hints for Possible Star–Planet Interaction

CoRoT-2a is a young (≈0.5 Gyr) G7V star accompanied by a transiting hot-Jupiter, discovered by the CoRoT satellite (Alonso et al. Astron Astrophys 482:L21, 2008; Bouchy et al. Astron Astrophys 482:L25, 2008). An analysis of its photospheric activity, based on spot modelling techniques previously developed by our group for the analysis of the Sun as a star, shows that the active regions on CoRoT-2a arised within two active longitudes separated by about 180° and rotating with periods of 4.5221 and 4.5543 days, respectively, at epoch of CoRoT observations (112 continous days centered at ≈2007.6). We show that the total spotted area oscillates with a period of about 28.9 days, a value close to 10 times the synodic period of the planet with respect to the active longitude pattern rotating in 4.5221 days. Moreover, the variance of the stellar flux is modulated in phase with the planet orbital period. This suggests a possible star–planet magnetic interaction, a phenomenon already seen in other extrasolar planetary systems hosting hot-Jupiters.     

Fostering sustainable tribal economies in a time of climate change

In this article, we explore how Māori tribal organisations are responding to calls by other Indigenous peoples to become more sustainable in a time of climate change. From a close examination of tribal Environmental Management Plans, we move to a specific case study in the Bay of Plenty area, Ngāti Kea/Ngāti Tuara. Ultimately, we suggest that many tribal organisations are seeking to respond to climate change and transition to becoming producers of their own food and energy needs, and are often articulating these responses in relation to specific local resources and contexts.     

Quantifying felt events: A joint analysis of intensities, accelerations and dominant frequencies

Recent seismic events for which macroseismic intensities and accelerometric records are simultaneously available are investigated in order to derive empirical relationships between intensities and ground accelerations. 20 events with local magnitudes 3.0 to 5.4 are selected in a single country (France), in order to have homogeneous intensity data. Records are obtained in about 50 stations. Relationships are first established between intensities, magnitudes and distances on one side, between S-wave horizontal peak ground accelerations (PGA), magnitudes and distances R on the other side. They show that the PGA decays with distance roughly as R ⁻², in agreement with previous studies, and that PGA and intensities lead to different attenuation models. An intensity-acceleration relationship is established from direct observations, and from a combination of the previous relationships. It reveals that the intensity felt depends not only on the PGAs, but also on the distance. This may be explained by the frequency dependent attenuation of the waves, and by a different sensitivity of humans to the different frequencies. The influence of frequency on the felt intensity is then investigated, and a relation between intensity, PGA and frequency is established. It shows that the acceleration needed to be felt with a given intensity is larger at high frequency than at low frequency.Finally, as sound also contributes to earthquake perception, the P-wave displacement is analysed in an attempt to find in which conditions a perceptible sound is generated. The perturbation in air pressure induced by the P-wave is compared to the threshold of hearing in two frequency ranges, 20–40 Hz and 40–60 Hz. The maximum distance of perceptibility as a function of magnitude deduced from the P-wave displacement alone is found to be below the experimental distances of perception reported in the macroseismic enquiries.