A detrital apatite fission‐track study of the CIROS‐2 sedimentary record: Tracing ice pathways in the Ross Sea area over the last 5 Ma

The Ross Sea is a crucial area to investigate pathways of ice during the Cenozoic as it records the evolution of both the East and West Antarctic Ice Sheets. This work is based on detrital apatite fission track (AFT) data extracted from the sedimentary record of well CIROS‐2, which spans the last 5 Ma. The AFT data show a large range of ages, and most of the grains fit well with two main components that fall between 24 and 42 Ma and between 43 and 70 Ma, whereas the other components are not regularly distributed through the well, thus indicating a mixture of provenance from different areas along the Transantarctic Mountains. As a whole, our work suggests glacial expansion over the McMurdo Sound during the Pliocene, and ice periodically invading and retreating in Pleistocene.     

Probabilistic seismic hazard model for Cairo,Egypt: estimates and uncertainties

A new seismic hazard model for Cairo, the capital city of Egypt is developed herein based on comprehensive consideration of uncertainties in various components of the probabilistic seismic hazard analysis. The proposed seismic hazard model is developed from an updated catalogue of historical and instrumental seismicity, geodetic strain rates derived from GPS-based velocity-field of the crust, and the geologic slip rates of active faults. The seismic source model consists of area sources and active faults characterised to forecast the seismic productivity in the region. Ground motion prediction models are selected to describe the expected ground motion at the sites of interest. The model accounts for inherent epistemic uncertainties of statistical earthquake recurrence; maximum magnitude; ground motion prediction models, and their propagation toward the obtained results. The proposed model is applied to a site-specific hazard analysis for Kottamiya, Rehab City and Zahraa-Madinat-Nasr (hereinafter referred to as Zahraa) to the East of Cairo (Egypt). The site-specific analysis accounts for the site response, through the parameterization of the sites in terms of average 30-m shear-wave velocity (Vs30). The present seismic hazard model can be considered as a reference model for earthquake risk mitigation and proper resilience planning.     

Industrial accidents triggered by earthquakes,floods and lightning: lessons learned from a database analysis

Natural hazards and disasters can cause major accidents in chemical and process installations. These so-called Natech accidents can result in hazardous-materials releases due to damage to process and storage units, or pipes. In order to understand the dynamics of Natech events, accidents triggered by earthquakes, floods and lightning recorded in industrial accident databases were analysed. This allowed the identification of the most vulnerable equipment types, their modes of failure due to natural-event impact and the final accident scenarios. Moreover, lessons learned for future accident prevention and mitigation were derived. The analysis showed that pipes and storage tanks are the most vulnerable equipment for earthquakes, floods and lightning, calling for more research of equipment behaviour under natural-event loading. The damage modes and states are strongly dependent on the characteristics of the impacting natural event. Toxic dispersion, fires and explosions were observed as a consequence of all three types of analysed natural events. In the case of floods, two additional scenarios were identified. These are water contamination and the formation of toxic and/or flammable vapours upon reaction of the released chemicals with the floodwaters. The overall number of recorded Natech accidents was found to range from 2 to 5% of all reported accidents in the analysed databases.     

Evidence of a full West Antarctic Ice Sheet back to the early Oligocene: insight from double dating of detrital apatites in Ross Sea sediments.

The West Antarctic Ice Sheet is the most unstable component of the Antarctic cryosphere. Its fluctuations are well documented since the Pliocene, but its behaviour over the last 35 Ma is more controversial, particularly during periods of past high global pCO₂ values similar to those predicted in future global climate scenarios. Here, we present new U–Pb dating of detrital apatite grains (previously dated by the fission‐track method) from Cape Roberts Project Oligocene to Pliocene marine sediments in the Ross Sea. Two past ice‐flow patterns were identified: one formed by outlet glaciers sourcing short‐travelled apatites and one, northerly directed, bringing far‐travelled apatite grains. The latter provides the first robust physical evidence for the presence and repeated expansion of an Oligocene West Antarctic Ice Sheet.     

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

The Middle-Upper Miocene Las Burras–Almagro-El Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes (∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma) is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma–water contact facies in the BAT volcanic sequence indicates the possible availability of water in the system between 11–7 Ma and suggests a depositional setting in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain that included extensive wetlands.     

Modal model identification of structures under unmeasured seismic excitations

Techniques developed for structural identification of a structural model are typically based on information regarding the response and the forcing actions. However, in some situations it can be necessary, or simply useful, to refer only to the measured responses. In this paper we describe a technique suitable for identifying the modal model of a spatial frame in the frequency domain when the seismic input is unknown both in time contents and direction. In some previous theoretical works we established that this identification problem has a unique solution when at least three time‐history responses are known. Here numerical techniques are developed which allow the evaluation of the modal quantities in practice. Numerical applications are carried out on plane and spatial framed structures by using a modal model which may be complete, including all the structure's modes, or incomplete, including only the lowest modes. In most cases the obtained results are satisfactory. Copyright © 2005 John Wiley & Sons, Ltd.     

Reproductive biology of the leatherjacket,Meuschenia scaber (Monacanthidae) (Forster 1801) in the Hauraki Gulf,New Zealand

The leatherjacket Meuschenia scaber is widely distributed in Australasian waters, and is a valued bycatch of inshore bottom trawl fisheries although little is known of its life history. Here, we describe the reproductive biology of the species based on 651 leatherjackets sampled in the Hauraki Gulf, New Zealand, between July 2014 and March 2016. The maximum total length (L_T) recorded for females and males were 320 and 315?mm, respectively, with both sexes present in all size classes. Monthly analysis of gonad condition revealed a clear spawning season from late austral winter to early summer (August–December), and histological analysis of the ovaries revealed that M. scaber is an indeterminate serial spawning gonochorist. The estimated sizes at sexual maturity (L₅₀) for females (189.9?mm L_T) and males (188.4?mm L_T) did not differ significantly. Relatively small testes, sexual dimorphism and underwater observation of nesting suggest that M. scaber is a paired spawner.     

Temporal variations in the spatial distribution of shoot density in a Posidonia oceanica meadow and patterns of genetic diversity

The meadows of the Mediterranean endemic seagrass Posidonia oceanica exhibit relatively high variations of structural and biometric features at various spatial scales. An investigation performed in 1992 in the meadow off Lacco Ameno (Island of Ischia, Gulf of Naples, Italy) detected peculiar spatial patterns of plant distribution, characterized by nestlike structures with radially increasing or decreasing shoot densities. Eight years later (2000), geo‐referenced collections at selected points were repeated to trace the temporal variations of shoot density and investigate the recurrence of the density cores previously detected. In addition, shoots for molecular analyses were collected to check the hypothesis that nestlike patterns exhibit highest levels of genetic variability, due to the confluence of several genetically distinct stolons. The 2000 survey confirmed the presence of the main density cores detected in 1992, although their spatial distribution was slightly shifted and a general decrease of spatial anisotropy was observed, probably due to an increased disturbance, mainly due to pleasure boat anchoring. Patterns of genetic diversity showed a more complex picture, well related to the shoot density spatial pattern, especially when compared with the previous 1992 survey. Patterns of genetic diversity confirmed our previous hypotheses on the genesis of shoot density cores, suggesting they are produced over long time, due to a slow stolonization process and a convergence of different genotypes. Regression of the meadow and decrease of density may lead, in short periods, to a homogenization of the density patterns, while genetic diversity cores represent a long‐term ‘memory’ of their previous distribution.