An approach for estimating the largest probable tsunami from far-field subduction zone earthquakes

Following the recent unexpected earthquake events of 2004 and 2011, it can be cautiously extrapolated that all major subduction zones bearing the capacity to produce mega-earthquake events will eventually do so given enough time, irrespective of the lack of such in the relatively short historical record. This notion has led to an effort of assigning maximum earthquake magnitudes to all major subduction zones, either based on geological constraints or based on size–frequency relations, or a combination of both. In this study, we utilize the proposed maximum magnitudes to assess tsunami hazard in Central California in the very long return periods. We also assessed tsunami hazard following an alternative methodology to calculate maximum magnitudes, which uses scaling relations for subduction zone earthquakes and maximum fault rupture scenarios found in literature. A sensitivity analysis is performed for Central California that is applicable to any coastal site in the Pacific Rim and can readily provide a strong indication for which subduction zones beam the most energy toward a study area. The maximum earthquake scenarios are then narrowed down to a few candidates, for which the initial conditions are examined in more detail. The chosen worst-case scenarios for Central California stem from the Alaska–Aleutian subduction zone that beams more energy and generates the biggest amplitude waves toward the study area. The largest tsunami scenario produces maximum free surface elevations of 15 m and run-up heights greater than 20 m.     

Upper Pleistocene to Holocene peatland evolution in Southern Brazilian highlands as depicted by radar stratigraphy,sedimentology and palynology

Paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs, in which peat accumulates in still environments. Reports on proxies obtained from minerotrophic fens, where hydrologic inputs are variable, are less common. In this study, a highland peatland in southern Brazil is presented through ground penetrating radar (GPR) and sedimentological, palynological and geochronologic data. The radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of Marine Isotope Stage 3 (MIS 3) interstadial period. In spite of this, radar stratigraphic and palynologic interpretations converge. Electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types, while pollen grains abound and are well preserved. As a result, the study of minerotrophic fens provides a source of proxies, suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis.     

Isotope geochemistry of Paleoproterozoic metacarbonates from Itatuba,Borborema Province,Northeastern Brazil: Evidence of marble melting within a collisional suture

Strongly-deformed marbles may be easily confused with linear and elongated carbonatite intrusions. Both rocks may present similar texture and foliation to the host rock, or even cross cutting field relationships, which could be interpreted either as igneous or high-grade metamorphosed marble. Diagnostic criteria are even more complex when there is evidence of melting of the metasedimentary carbonate rock, such as has been described in the Himalayas and in the Eastern Ghats, India.In the Alto Moxotó Terrane, a high-grade gneissic domain of the Borborema Province, Northeastern Brazil, there are metacarbonates associated with banded gneisses and different metaplutonic rocks. Field evidence indicates the absence of other metasedimentary rocks associated with these marbles, thus suggesting that these carbonates were separated from other siliciclastic metasedimentary rocks. The presence of marble also suggests that it may represent the initial stage of a crustal carbon recycling into the mantle. These marbles present many field similarities to carbonatites (e.g., fluid-flow structure) and, together with metagranites and metamafic intrusions, may represent a major collisional tectonic suture.A detailed study of the carbon, oxygen and strontium isotopic composition of these marbles is presented. This study aims to identify the origin of the different isotopic components. It is argued that these rocks were subjected to temperature and pressure conditions that were sufficiently high to have melted them. The isotopic data presented here support this interpretation and indicate the mixing of two components: (i) one characterized by radiogenic Sr isotopes and mantle-like carbon isotopes, which is associated with the gneissic and mafic rocks, and (ii) another characterized by low ⁸⁷Sr/⁸⁶Sr ratios and highly positive δ¹³C values. Available geochemical data for the upper Paleoproterozoic indicate that the ⁸⁷Sr/⁸⁶Sr ratio of ocean water, varying between 0.7050 (2.25 ± 0.25 Ga) and 0.7047 (1.91 Ga), falls within the lower range of the samples from Itatuba and thus reinforces the interpretation that these marbles are sedimentary-derived and were partially contaminated by interaction with the host gneissic and mafic rocks.     

Impact of irrigated agriculture on groundwater-recharge salinity: a major sustainability concern in semi-arid regions

Intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts. The article focuses upon a specific concern—the tendency for progressive long-term increases in the salinity of groundwater recharge derived from irrigated permeable soils and replenishment of unconfined aquifers in more arid regions. This process has received only scant attention in the water-resource literature and has not been considered by agricultural science. This work makes an original contribution by analysing, from scientific principles, how the salinisation of groundwater recharge arises and identifies the factors affecting its severity. If not proactively managed, the process eventually will impact irrigation waterwell salinity, the productivity of agriculture itself, and can even lead to land abandonment. The types of management measure required for mitigation are discussed through three detailed case histories of areas with high-value groundwater-irrigated agriculture (in Spain, Argentina and Pakistan), which provide a long-term perspective on the evolution of the problem over various decades.     

Integrating Stalagmite, Vertebrate, and Pollen Sequences to Investigate Holocene Vegetation and Climate Change in the Southern Midwestern United States

Speleothem carbon and oxygen isotopic records from Onondaga Cave, south-central Missouri, and Beckham Creek Cave, north-central Arkansas, are compared with the Cupola Pond and Oldfield Swamp pollen series from southeastern Missouri and the Rodgers Shelter and Modoc Shelter vertebrate biostratigraphic sequences from central Missouri and southwestern Illinois. Similar, and roughly contemporaneous, shifts between deciduous forest and steppe indicators throughout the Holocene are revealed in each database. These independent proxies record steppe conditions between approximately 9000 and 1500 cal yr B.P. A shift toward lighter speleothem carbon may reflect a change from warm and dry to cool and dry conditions between 4500 and 3000 yr B.P. The sensitive response of speleothem δ¹³C to changes in vegetation emphasizes their importance as paleoclimate records in an area containing few other millenial-scale climate proxies.     

Computer simulation studies of Crystallization under confinement conditions

Crystallization under confinement conditions is a very important process in geochemistry and geophysics. Computer simulations of fluids in nanometer scale pore spaces can provide a unique microscopic insight into the structure, dynamics and forces arising from the crystallization process. We discuss in this paper molecular dynamics computer simulations of crystallization in pores of nanometer dimensions. The crystallization pressure due to the freezing of a model of Argon in a nanopore is computed using molecular dynamics simulations. We also investigate the influence of pore geometry in determining the dynamics of confined fluids, as well as mass separation in binary mixtures. It turns out that the pore geometry reveals itself as an important variable, leading to 1) new mechanisms for fast diffusion in confined spaces, and 2) accumulation of solute in specific regions inside the pore.     

Mobilization analysis of the dolmen of Dombate (Northwest Spain)

This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monument situated in the Northwest of Spain. The study is founded on simple static principles, with the application of basic concepts of soil mechanics (soil reactions were computed by the reaction modulus method) and rock mechanics (a simple secant approach was adopted to model the contact between orthostats). In addition, a simplified geometric model for dolmens was adopted. On the basis of these concepts, a numerical solver able to provide quick estimations of the system's mobilization was developed. Using this tool, a number of sensitivity analyses were conducted to estimate the mobilization that could be caused by a conservation project currently under consideration. It was found that mobilization might be excessive, and therefore, a safer procedure is proposed. In short, this paper puts forth a new rational approach for archaeological practices which may help to estimate the possible consequences of excavations and rehabilitations on megalithic structures.     

Dynamics of MTBE-degrading activity in porous media using a large-scale laboratory experiment

Methyl tert-butyl ether (MTBE) is an oxygenated organic compound that tends to form large groundwater contamination plumes. If bioaugmentation is used as a remediation technique, the question of the mobility of the bioactive zone (BAZ) with time is of interest. The objective of this experiment was to study the spatial redistribution of MTBE-biodegradation activity through time, following the injection of a bacterial culture in a homogeneous porous media, at high pressures and concentrations. The experiment was performed using a large-scale aquifer physical model, which can incorporate physicochemical heterogeneities similar to those found in the field, under controlled laboratory conditions. The experimental tank was filled with 1.0-mm-diameter glass beads to represent a homogeneous high hydraulic conductivity porous medium. During inoculation, the bacterial culture was distributed in a circular pattern. Initially it appeared that the BAZ was located in the upstream portion of the inoculated zone, where oxygen was available in conjunction with the inoculated bacteria and MTBE. With time, the BAZ moved upgradient through the whole tank towards the inlet. This implies the successful movement of bacteria from the inoculation area against advective flow into previously sterile zones of the tank. A mass balance showed that dissolved oxygen concentrations were likely not a limiting factor during the experiments.