GIS-based analysis of foundation repairs and soil conditions in the Dallas-Fort Worth region,Texas

The Dallas-Fort Worth region is subject to a severe expansive soils hazard, resulting in costly damage to many thousands of residential foundations each year. A GIS is used to examine relationships between a sample of approximately 10,000 foundation repair addresses and geologic and soil conditions. The study results show that foundation repairs are concentrated in areas underlain by bedrock, surficial deposits and soils that promote high shrink–swell potentials. A linear extensibility index, designed as an index of overall shrink–swell potential explains about 48% of the variation in the prevalence of repairs. Repairs are concentrated on soils that underlay many areas of new urban growth in the DFW region, suggesting that the incidence of foundation repairs in these areas will probably increase in the future. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Slab dehydration and basalt petrogenesis in subduction systems involving very young oceanic lithosphere

Compositions of post-Miocene basalts erupted in the Garibaldi and Central America volcanic arcs exhibit significant correlations with the age of the subducted plate. In general, SiO₂, Al₂O₃, CaO, V, and (Sr/P)_N decrease and FeO, MgO, TiO₂ and Na₂O increase as the age of the subducted plate decreases. Variations in CaO/Al₂O₃, SiO₂, (Sr/P)_N, and Ba are compatible with lesser slab input, and hence less hydrous melting conditions in the mantle wedge in segments of the arcs overlying the youngest oceanic lithosphere. This interpretation is supported by comparison with peridotite melting experiments, which suggest higher melt pressures and temperatures in the mantle wedge above very young oceanic lithosphere. These observations point to a model in which dehydration of the downgoing slab occurs at shallow depths in subduction systems involving oceanic lithosphere younger than about 20 Ma. Because young oceanic lithosphere is relatively warm, little post-subduction heating is required to produce metamorphic reactions that release slab volatiles. Geodynamic models indicate most volatile-liberating reactions will occur within the seismogenic zone in oceanic lithosphere younger than 20 Ma, thus limiting the volatile flux beneath the arc and encouraging drier, higher temperature and higher pressure melting conditions in the mantle wedge in comparison to typical arc systems. Liberation of volatiles in the downgoing plate is strongly dependant on the shear stress on the fault, but is predicted to occur within the seismogenic zone for shear stresses greater than 33 MPa. Similarly, early loss of volatiles is predicted over a wide range of convergence rates, plate dips, and convergence angles. These results are shown to be robust for realistic ranges of slab dip, convergence angle, and shear stress, suggesting that volatile-poor melt generation is a characteristic of modern and ancient arc systems that involve subduction of young oceanic lithosphere.     

Chaos in three-body dynamics: Kolmogorov–Sinai entropy

An ensemble of Newtonian three-body models with close initial separations is investigated by following the evolution of a 'drop' in the homology map. The onset of chaos is revealed by the motion and the complex temporal deformation of the drop. In the state of advanced chaos, the drop spreads over almost the whole homology map, quite independently of its initial position on the map. A general quantitative measure of this process is the mean exponential rate of spreading, which bears resemblance to Kolmogorov–Sinai entropy; this is introduced and estimated in terms of the homology mapping. In a similar manner we also estimate the mean exponential rate of divergence of initially close-by trajectories. This is a close analogue to the Lyapunov exponent. These parameters measure two complementary aspects of dynamical instability, which is the basic mechanism of the onset of chaos.     

Dacite formation on Vesta: Partial melting of the eucritic crust

The Dominion Range 2010 howardite pairing group contains an evolved lithic clast of dacite composition. The dacite contains an assemblage of plagioclase, quartz, and augite, with minor pigeonite, troilite, ilmenite, FeNi metal, K‐feldspar, and phosphates. Primary augite occurs as >1 mm oikocrysts enclosing plagioclase. Quartz is abundant, comprising approximately 30% of the clast. Textural and geochemical characteristics support the hypothesis that the dacite is a primary igneous lithology, and represents a partial melt of the eucritic crust. Numerical modeling (MELTS) suggests 10–20% partial melting of a Juvinas source could have produced the dacite lithology; quantitative trace element modeling further supports crustal partial melting as the magma source for the dacite. The dacite likely formed as evolved‐melt pockets, and thus represents a volumetrically minor lithology in the Vestan crust, although its formation provides direct support for a genetic relationship between Stannern and residual trend eucrites, and is the first identification of residual eucrite complementary melts. We propose the dacite clast is the first characterized sample of tertiary crust on Vesta.     

Seasonal prediction of the Leeuwin Current using the POAMA dynamical seasonal forecast model

The potential for predicting interannual variations of the Leeuwin Current along the west coast of Australia is addressed. The Leeuwin Current flows poleward against the prevailing winds and transports warm-fresh tropical water southward along the coast, which has a great impact on local climate and ecosystems. Variations of the current are tightly tied to El Niño/La Niña (weak during El Niño and strong during La Niña). Skilful seasonal prediction of the Leeuwin Current to 9-month lead time is achieved by empirical downscaling of dynamical coupled model forecasts of El Niño and the associated upper ocean heat content anomalies off the north west coast of Australia from the Australian Bureau of Meteorology Predictive Ocean Atmosphere Model for Australia (POAMA) seasonal forecast system. Prediction of the Leeuwin Current is possible because the heat content fluctuations off the north west coast are the primary driver of interannual annual variations of the current and these heat content variations are tightly tied to the occurrence of El Niño/La Niña. POAMA can skilfully predict both the occurrence of El Niño/La Niña and the subsequent transmission of the heat content anomalies from the Pacific onto the north west coast.     

Pyroxene thermobarometry in LL-group chondrites and implications for parent body metamorphism

Abstract— Geothermometry based on the compositions of clinopyroxenes in type 6 and 7 LL chondrites gives coherent results, but the estimated temperatures from coexisting orthopyroxenes are consistently lower than for clinopyroxenes. Orthopyroxene thermometry is suspect because of compositional effects of polymorphic inversions and/or unknown kinetic factors. Lack of clinopyroxene equilibration precludes accurate estimation of peak metamorphic temperatures for type 4 and 5 chondrites. There is no apparent correlation between Al content (a pressure-dependent variable) and equilibration temperature in chondritic pyroxenes. This finding, which is at variance with a previously published conclusion that temperature and pressure are correlated in metamorphosed chondrites, may have important implications for asteroid thermal models.     

Tsunami bore runup

Nearshore behaviors of tsunamis, specifically those formed as a single uniform bore, are investigated experimentally in a laboratory environment. The transition process from tsunami bore to runup is described by the momentum exchange process between the bore and the small wedge-shaped water body along the shore: the bore front itself does not reach the shoreline directly, but the large bore mass pushes the small, initially quiescent water in front of it. The fluid motions near the runup water line appear to be complex. The complex flow pattern must be caused by irregularities involved in the driving bore and turbulence advected into the runup flow. Those experimental results suggest that the tsunami actions at the shoreline involve significant mean kinetic energy together with violent turbulence. Even though the behaviors of bore motion were found to be different from those predicted by the shallow-water wave theory, the maximum runup height appears to be predictable by the theory if the value of the initial runup velocity is modified (reduced). Besides the friction effect, this reduction of the initial runup velocity must be related to the transition process as well as the highly interacting three-dimensional runup motion.