Geospace perturbations induced by the Earth: The state of the art and future trends

A systematic multi-parameter and multi-platform approach to study the slow process of earthquake preparation is fundamental to gain some insights on this complex phenomenon. In particular, an important contribution is the integrated analysis between ground geophysical data and satellite data. In this paper we review some of the more recent results and suggest the next directions of this kind of research. Our intention is not to detect a particular precursor but to understand the physics underlying the various observations and to establish a reliable physical model of the preparation phase before an impending earthquake. In this way, future investigation will search for suitable fore-patterns, which the physical model of multi-layers coupling predicts and characterizes by quasi-synchronism in time and geo-consistency in space. We also present alternative explanations for some anomalies which are not actually related to earthquakes, rather to other natural or anthropic processes.     

Socioeconomic impacts of hydropower development on the Yibin–Chongqing section,upper reaches of the Yangtze River

The aim of this paper is to quantify the socioeconomic impacts of hydropower development to reflect its positive functions from multiple perspectives and dimensions. By applying the multi-regional Computable General Equilibrium (CGE) model to a case study of the Yibin–Chongqing section along the upper reaches of the Yangtze River, the analysis shows that hydropower development has outstanding benefits for the regional economy and livelihood improvement, as proved by various indicators including consumption, investment, GDP, employment, and income. Meanwhile, application of the CGE model provides an effective way to quantitatively assess the socioeconomic impact of hydropower and other clean energy development.     

Food web and fish stock changes in central Chile: comparing the roles of jumbo squid (Dosidicus gigas) predation,the environment,and fisheries

We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978–2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts.     

Three-dimensional dynamic response of multilayered poroelastic media

ABSTRACT

The dynamic response of a multilayered poroelastic medium under 3D time-harmonic loading is studied using an exact stiffness method. The poroelastic medium under consideration consists of N layers of different thicknesses and properties and an underlying poroelastic half-space. The exact stiffness matrices for each layer and the underlying half-space are derived explicitly using Biot’s poroelastodynamic theory and double-dimensional Fourier transforms. Selected numerical results are presented to demonstrate the influence of various parameters on dynamic response of multilayered poroelastic media under traction and fluid loading. The application of proposed solution scheme to soil–structure interaction problems is also presented.     

Centrifuge modelling of lateral loading behaviour of a “semi-rigid” Mono-pile in soft clay

Abstract

Mono-pile foundations have been widely used for offshore wind turbines principally due to their convenient construction and cost-effective nature. So far, little attention has been paid to large diameter “semi-rigid” piles that have distinct behaviours from flexible or ideally rigid piles. This paper presents a series of centrifuge model tests to study the deforming and bearing characteristics of a 5.9 dia. semi-rigid pile under lateral loadings in kaolin clay. For monotonic loading, a modified p–y curve analysis model considering rotational soil flow near the rotation centre of pile was proposed, highlighting the limitation of classic plane-strain based plasticity models to evaluate the ultimate lateral pile-soil resistance. For cyclic loading, a strong correlation between the degree of soil degradation and cyclic load amplitude was identified. Besides, a degradation factor model, accounting for various cyclic stress levels and soil depths, was proposed, which can be used to assess the accumulative displacement of semi-rigid piles under cyclic loadings in soft clay.     

Decisions of the U. S. Board of Geographic Names. June 5, 1900, To January 8, 1902 II

ABSTRACT

Spatial literacy is a new frontier in K–12 education. This article describes a place-based introductory GIS/GPS middle school curriculum unit in which students used measuring tools, GPS units, and My World GIS software to collect physical and spatial data of trees to create a schoolyard tree inventory. Maine students completed “memory maps” of their schoolyards as a pre/post exercise assessment. A statistically significant increase in students’ spatial awareness was documented. A technology-based curriculum can significantly increase students’ spatial awareness especially in a place and context relevant to each student.     

Geology and geochemistry of the Jianchaling hydrothermal nickel deposit: T–pH–fO2–fS2 conditions and nickel precipitation mechanism

The Jianchaling nickel deposit in the Bikou Terrane (Shaanxi Province, China) occurs along the boundaries between granite porphyry and carbonated ultramafic rocks (carbonated serpentinite, talc–carbonate rocks, and listwaenite). Serpentine– magnetite, serpentine– magnesite– magnetite, and magnesite– talc– quartz– pyrite– violarite– millerite– chalcopyrite assemblage formed in carbonated ultramafic rocks during hydrothermal activities. Ni-bearing sulphides, coexisting with magnesite, postdated magnetite in carbonated ultramafic rocks. Compared with serpentinite, Ni, Co, Cu, Mn, and Pb concentrate in talc–carbonate rocks. The fact that the NiO contents of magnetite decrease with progressive carbonation of serpentinite suggests that Ni from magnetite concentrated in fluid and contributed to the formation of the Jianchaling nickel deposit. Sulphides precipitated from fluid with log fO₂ value varying from −34.5 to −31.8 and log fS₂ value varying from −10.3 to −9.2. High pH and HS⁻ activities triggered by transformation of serpentine into magnesite–talc–quartz assemblage promoted precipitation of Ni-bearing sulphides, and finally formed the Jianchaling hydrothermal nickel deposit.     

Petrogenesis and zircon LA-ICP-MS U–Pb dating of newly discovered Mesoarchean gneisses on the northern margin of the North China Craton

Geological mapping and zircon U–Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) dating has identified a Mesoarchean (2857 ± 17 Ma) geological unit in the Luanjiajie area of the northern margin of the North China Craton, within the northern part of Liaoning Province, China. This unit is dominated by tonalitic and trondhjemite gneisses that form part of a typical tonalite–trondhjemite–granodiorite (TTG) rock assemblage. These Mesoarchean gneisses are enriched in Na and depleted in K, yield K₂O/Na₂O ratios of 0.34–0.50, have Rittmann index (σ) values of 1.54–3.04, and are calc-alkaline. They have Eu_N/Eu_N* values of 0.77–1.20 (average of 1.03), indicating that these samples have negligible Eu anomalies, and yield high La_N/Yb_N values (4.92–23.12). These characteristics indicate that these Mesoarchean gneisses have fractionated rare earth element (REE) compositions that are enriched in the light REE (LREE) and depleted in the heavy REE (HREE), with steeply dipping chondrite-normalized REE patterns. These gneisses are also enriched in Rb, Th, K, Zr, and Hf, and are relatively depleted in Ta, Nb, P, and Ti. In summary, the magma that formed these tonalitic and trondhjemite gneisses was most likely derived from the partial melting of lower-crustal basaltic rocks during subduction. The timing of formation (2.85 Ga) of the Luanjiajie tonalite and trondhjemite gneisses probably represents the timing of initiation of plate tectonics within the LongGang Block during a SE-directed subduction event. The presence of inherited zircons with ages of >3.0 Ga within the Luanjiajie gneisses suggests that this area may contain as yet undiscovered rocks that formed before 3.0 Ga.     

Late Oligocene–Miocene mantle upwelling and interaction inferred from mantle signatures in gabbroic to granitic rocks from the Urumieh–Dokhtar arc,south Ardestan,Iran

The south Ardestan plutonic rocks constitute major outcrops in the central part of Iran’s Cenozoic magmatic belt and encompass a wide compositional spectrum from gabbro to granodiorite. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating of zircon three granodiorites yielded ages of 24.6 ± 0.1, 24.6 ± 0.1, and 24.5 ± 0.1 Ma. For tonalitic rocks, internal Rb–Sr isochron ages (biotite, feldspars) indicate cooling ages of 20.4 ± 0.1, 20.5 ± 0.1, and 22.3 ± 0.1 Ma, which are slightly younger than the zircons’ ages. The limited variations in their Sr–Nd isotope ratios indicate derivation from an asthenospheric mantle source. A geodynamic model is presented in which late Oligocene–Miocene rollback of the Neotethyan subducting slab triggered asthenospheric upwelling and partial melting in the south Ardestan. These melts were subsequently modified through fractional crystallization and minor crustal contamination en-route to the surface. Plagioclase + orthopyroxene-dominated fractional crystallization accounts for differentiation of gabbro to gabbroic diorite, whereas fractionation of clinopyroxene, titanomagnetite, and orthopyroxene led to differentiation of gabbroic diorite to diorite. Amphibole fractionation at deeper levels led to the development of tonalites.