The northern Patagonia Somuncura plateau basalts: a product of slab‐induced,shallow asthenospheric upwelling?

The Meseta de Somuncura forms the largest basaltic plateau (20 000 km²) of southern Argentina (extra-Andean domain). Most of these tholeiitic to alkaline rocks were extruded at ˜ 25 Ma (late Oligocene). The absence of rifting–thinning processes, plume activity, or slab-window phenomena leaves only one major possibility for the generation of Somuncura: asthenospheric ('OIB-like') corner flow leading to a transient thermal anomaly above the subducting plate. It is suggested herein that the intake of hot asthenosphere was forced into a favourable topography (concave-up) of the subducting plate, when a major plate reorganization event (Farallon to Nazca) was taking place in late Oligocene to early Miocene time. The fast and vigorous intake of asthenosphere would have been induced by slab roll-back, leading to decoupling of the subducting plate. The Somuncura volcanic episode can be regarded as a marker of the passage from the extremely oblique subduction of Farallon, to the birth of the Nazca plate and roughly perpendicular convergence between South America and Nazca.     

A seismic source zone model for the seismic hazard assessment of the Italian territory

We designed a new seismic source model for Italy to be used as an input for country-wide probabilistic seismic hazard assessment (PSHA) in the frame of the compilation of a new national reference map.

We started off by reviewing existing models available for Italy and for other European countries, then discussed the main open issues in the current practice of seismogenic zoning.

The new model, termed ZS9, is largely based on data collected in the past 10 years, including historical earthquakes and instrumental seismicity, active faults and their seismogenic potential, and seismotectonic evidence from recent earthquakes. This information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model ZS4.

ZS9 is made out of 36 zones where earthquakes with M_w > = 5 are expected. It also assumes that earthquakes with M_w up to 5 may occur anywhere outside the seismogenic zones, although the associated probability is rather low. Special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates.

Although it was drawn following criteria that are standard practice in PSHA, ZS9 is also innovative in that every zone is characterised also by its mean seismogenic depth (the depth of the crustal volume that will presumably release future earthquakes) and predominant focal mechanism (their most likely rupture mechanism). These properties were determined using instrumental data, and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications. These attributes allow ZS9 to be used with more accurate regionalized depth-dependent attenuation relations, and are ultimately expected to increase significantly the reliability of seismic hazard estimates.     

Diagenesis, palaeoclimate and tectono-sedimentary influences on clay mineralogy and stable isotopes from Upper Cretaceous marine successions of the Basque-Cantabrian Basin (N Spain)

Clay mineralogy and whole-rock stable isotopes (δ¹⁸O and δ¹³C) of Upper Cretaceous marly sediments on the Basque-Cantabrian Basin have been integrated to determine the main effects of diagenesis, palaeoclimate and tectono-sedimentary factors in sections belonging to deep- (Barrika) and platform-marine (Isla de Castro, Villamartín and Olazagutía) settings.The mean values for the clay assemblages and δ¹⁸O exhibit notable differences among the sections, partially explainable by the influence of diagenesis. The Barrika sediments, with more diagenetically advanced illite-smectite (I-S) mixed-layer (R1, 70% illite), authigenic chlorite, and low δ¹⁸O (−4.05‰ PDB), experienced higher diagenetic grade than Isla de Castro and Olazagutía, which have R0 I-S (20% illite) and heavier δ¹⁸O. Villamartín was also affected by higher diagenesis than Isla de Castro and Olazagutía, given the occurrence of R1 I-S (60% illite) and low δ¹⁸O (−4.11‰ PDB). However, the absence of other clays in Villamartín (e.g. authigenic chlorite) is indicative of less diagenetic grade than Barrika. These results show the useful integration of clay mineralogy and stable isotopes to detect different diagenetic grades in distinct marine successions of the same basin.Despite being influenced by diagenesis, the clay mineralogy partially preserves its inherited signature. This allows detection of major contents of I-S and mica, and minor kaolinite, interpreted as indicative of warm palaeoclimatic conditions. High kaolinite content in Villamartín and absence of kaolinite in Isla de Castro, though, are considered to be a product of neither diagenesis nor palaeoclimatic influences. Instead, tectono-sedimentary causes, related to unsuitable conditions for clay formation and transport from the local source areas, contributed to original clay differences. The inferred effects of diagenesis, palaeoclimate and tectono-sedimentary factors make this work important to show the potentially great variety of controls on the clay mineralogy of marine sections, which are often uncritically treated in studies concerning the Late Cretaceous.     

Origins of high pH mineral waters from ultramafic rocks, Central Portugal

This paper reviews the geochemical, isotopic (²H, ¹⁸O, ¹³C, ³H and ¹⁴C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO₃ type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ²H and δ¹⁸O suggest a common meteoric origin and that the Mg–HCO₃ type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO₃ to Mg–HCO₃ waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO₂ (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of ¹⁴C and ¹³C values, which is in agreement with the ³H concentrations being below the detection limit.     

Methodology for preliminary assessment of Natech risk in urban areas

Concern for natural hazard-triggered technological disasters (Natech disasters) in densely populated and industrialized areas is growing. Residents living in urban areas subject to high natural hazard risk are often unaware of the potential for secondary disasters such as hazardous materials releases from neighboring industrial facilities, chemical storage warehouses or other establishments housing hazardous materials. Lessons from previous disasters, such as the Natech disaster during the Kocaeli earthquake in Turkey in 1999 call for the need to manage low frequency/high consequence events, particularly in today’s densely populated areas. However, there is little guidance available on how local governments and communities can assess Natech risk. To add to the problem, local governments often do not have the human or economic resources or expertise to carry out detailed risk assessments. In this article, we propose a methodology for preliminary assessment of Natech risk in urban areas. The proposed methodology is intended for use by local government officials in consultation with the public. The methodology considers possible interactions between the various systems in the urban environment: the physical infrastructure (e.g., industrial plants, lifeline systems, critical facilities), the community (e.g., population exposed), the natural environment (e.g., delicate ecosystems, river basins), and the risk and emergency management systems (e.g., structural and nonstructural measures). Factors related to vulnerability and hazard are analyzed and qualitative measures are recommended. Data from hazardous materials releases during the Kocaeli, Turkey earthquake of August 17, 1999 are used as a case study to demonstrate the applicability of the methodology. Limitations of the proposed methodology are discussed as well as future research needs.

The Distribution of Amphipoda in a Brackish-Water Lagoon in Greece

Abstract. The distribution of the benthic Amphipoda was studied in the brackish-water lagoon Mazoma of Amvrakikos Bay, Ionian Sea, Greece. Eleven amphipod species typical of the sublittoral zone, some with preference for enclosed bays and lagoons, were identified. Gammarus crinicornis, Microdeutopus bifidus, C. rotundirostris , and Erichthonius difformis are mentioned for the first time for Greek waters. The distribution of amphipods in the lagoon is governed by the vegetation and is probably modified by interspecific relations.