Deformation produced by oblique rifting

With oblique rifting, both extension perpendicular to the rift trend and shear parallel to the rift trend contribute to rift formation. The relative amounts of extension and shear depend on α, the acute angle between the rift trend and the relative displacement direction between opposite sides of the rift. Analytical and experimental (clay) models of combined extension and left-lateral shear suggest the fault patterns produced by oblique rifting. If α is less than 30°, conjugate sets of steeply dipping strike-slip faults form in rifts. Sinistral and dextral strike-slip faults trend subparallel and at large angles to the rift trend, respectively. If α is about 30°, strike-slip, oblique-slip and/or normal faults form in rifts. Faults with sinistral and dextral strike slip trend subparallel and at large angles to the rift trend, respectively. Normal faults strike about 30° counterclockwise from the rift trend. If α exceeds 30°, normal faults form in rifts. They have moderate dips and generally strike obliquely to the rift trend and to the relative displacement direction between opposite sides of the rift. If α equals 90°, the normal faults strike parallel to the rift trend and perpendicularly to the displacement direction.The modeling results apply to the Gulf of California and Gulf of Aden, two Tertiary continental rift systems produced by combined extension and shear. Our results explain the presence and trends of oblique-slip and strike-slip faults along the margins of the Gulf of California and the oblique trend (relative to the rift trend) of many normal faults along the margins of both the Gulf of California and the Gulf of Aden.     

Origin of fault domains and fault-domain boundaries (transfer zones and accommodation zones) in extensional provinces: Result of random nucleation and self-organized fault growth

In many extensional provinces, large normal faults dip in the same direction forming fault domains. Features variously named transfer faults, transfer zones, and accommodation zones (hereafter non-genetically referred to as fault-domain boundaries) separate adjacent fault domains. Experimental modeling of distributed extension provides insights on the origin, geometry, and evolution of these fault domains and fault-domain boundaries. In our scaled models, a homogeneous layer of wet clay or dry sand overlies a latex sheet that is stretched orthogonally or obliquely between two rigid sheets. Fault domains and fault-domain boundaries develop in all models in both map view and cross-section. The number, size, and arrangement of fault domains as well as the number and orientation of fault-domain boundaries are variable, even for models with identical boundary conditions. The fault-domain boundaries in our models differ profoundly from those in many published conceptual models of transfer/accommodation zones. In our models, fault-domain boundaries are broad zones of deformation (not discrete strike-slip or oblique-slip faults), their orientations are not systematically related to the extension direction, and they can form spontaneously without any prescribed pre-existing zones of weakness. We propose that fault domains develop because early-formed faults perturb the stress field, causing new nearby faults to dip in the same direction (self-organized growth). As extension continues, faults from adjacent fault domains propagate toward each another. Because opposite-dipping faults interfere with one another in the zone of overlap, the faults stop propagating. In this case, the geometry of the domain boundaries depends on the spatial arrangement of the earliest formed faults, a result of the random distribution of the largest flaws at which the faults nucleate.     

Numerical study of baroclinic tides in Luzon Strait

The spatial and temporal variations of baroclinic tides in the Luzon Strait (LS) are investigated using a three-dimensional tide model driven by four principal constituents, O₁, K₁, M₂ and S₂, individually or together with seasonal mean summer or winter stratifications as the initial field. Barotropic tides propagate predominantly westward from the Pacific Ocean, impinge on two prominent north-south running submarine ridges in LS, and generate strong baroclinic tides propagating into both the South China Sea (SCS) and the Pacific Ocean. Strong baroclinic tides, ∼19 GW for diurnal tides and ∼11 GW for semidiurnal tides, are excited on both the east ridge (70%) and the west ridge (30%). The barotropic to baroclinic energy conversion rate reaches 30% for diurnal tides and ∼20% for semidiurnal tides. Diurnal (O₁ and K₁) and semidiurnal (M₂) baroclinic tides have a comparable depth-integrated energy flux 10–20 kW m⁻¹ emanating from the LS into the SCS and the Pacific basin. The spring-neap averaged, meridionally integrated baroclinic tidal energy flux is ∼7 GW into the SCS and ∼6 GW into the Pacific Ocean, representing one of the strongest baroclinic tidal energy flux regimes in the World Ocean. About 18 GW of baroclinic tidal energy, ∼50% of that generated in the LS, is lost locally, which is more than five times that estimated in the vicinity of the Hawaiian ridge. The strong westward-propagating semidiurnal baroclinic tidal energy flux is likely the energy source for the large-amplitude nonlinear internal waves found in the SCS. The baroclinic tidal energy generation, energy fluxes, and energy dissipation rates in the spring tide are about five times those in the neap tide; while there is no significant seasonal variation of energetics, but the propagation speed of baroclinic tide is about 10% faster in summer than in winter. Within the LS, the average turbulence kinetic energy dissipation rate is O(10⁻⁷) W kg^{− 1} and the turbulence diffusivity is O(10⁻³) m²s⁻¹, a factor of 100 greater than those in the typical open ocean. This strong turbulence mixing induced by the baroclinic tidal energy dissipation exists in the main path of the Kuroshio and is important in mixing the Pacific Ocean, Kuroshio, and the SCS waters.     

The influence of solar‐induced thermal stresses on the mechanical weathering of rocks in humid mid‐latitudes

The role of solar‐induced thermal stresses in the mechanical breakdown of rock in humid‐temperate climates has remained relatively unexplored. In contrast, numerous studies have demonstrated that cracks in rocks found in more arid mid‐latitude locations exhibit preferred northeast orientations that are interpreted to be a consequence of insolation‐related cracking. Here we hypothesize that similar insolation‐related mechanisms may be efficacious in humid temperate climates, possibly in conjunction with other mechanical weathering processes. To test this hypothesis, we collected rock and crack data from a total of 310 rocks at a forested field site in North Carolina (99 rocks, 266 cracks) and at forested and unforested field sites in Pennsylvania (211 rocks, 664 cracks) in the eastern United States. We find that overall, measured cracks exhibit statistically preferred strike orientations (47° ± 16), as well as dip angles (52° ± 24°), that are similar in most respects to comparable datasets from mid‐latitude deserts. There is less variance in strike orientations for larger cracks suggesting that cracks with certain orientations are preferentially propagated through time. We propose that diurnally repeating geometries of solar‐related stresses result in propagation of those cracks whose orientations are favorably oriented with respect to those stresses. We hypothesize that the result is an oriented rock heterogeneity that acts as a zone of weakness much like bedding or foliation that can, in turn, be exploited by other weathering processes. Observed crack orientations vary somewhat by location, consistent with this hypothesis given the different latitude and solar exposure of the field sites. Crack densities vary between field sites and are generally higher on north‐facing boulder‐faces and in forested sites, suggesting that moisture‐availability also plays a role in dictating cracking rates. These data provide evidence that solar‐induced thermal stresses facilitate mechanical weathering in environments where other processes are also likely at play. Copyright © 2015 John Wiley & Sons, Ltd.     

III. Mitteilung. Die hydrothermale Zersetzung des Peridotits bei der Bildung der Magnesitlagerstätte am Galgenberg bei Zobten

Ohne ZusammenfassungAbgeschlossen im Juni 1947.     

Life histories of large,grazing copepods in a subarctic ocean gyre: Neocalanus plumchrus,Neocalanus cristatus, and Eucalanus bungii in the Northeast Pacific

Life histories for the dominant, larger copepods of the subartic Pacific have been constructed by sampling from weatherships patrolling Ocean Station P (50°N, 145°W) during 1980 and 1981. Neocalanus plumchrus reproduced at depths below 250 m from July through February. Copepodite stages were present in surface layers from October through August with a large peak in numbers and biomass in spring. Fifth copepodites prepared for diapuse in 38 days during spring and descended to depths below 250 m. They commenced immediately to mature, and the females reproduced without renewed feeding. This schedule contrasts with that of the population in the Strait of Georgia, which remains in diapause from July to January and matures exclusively in January and February. There appears to be a difference between the coastal and oceanic habitats in preparing the diapausing individuals for maturation.Maturation of the diapausing stock of N. plumchrus maintained constant adult populations, averaging 714 males m^?2 from June through October and 1,434 females m^?2 from August through January. This constancy, together with the exponential pattern of decline in the diapause stock from September through February, suggests that density of adults may regulate maturation of fifth copepodites. Offspring of individuals delaying maturation and, thus, reproduction would benefit from the resulting moderation of intraspecific competition, probably that among copepodites.Reproduction of Neocalanus cristatus also occurred below 250 m, and, while spawning was continuous through the year, there was a substantial peak in November. That resulted in a peak of abundance for early copepodite stages in mid-winter, and a peak for the fifth copepodite stage in June. Stocking of the population of fifth copepodites in diapause below 250 m occurred from July through October. Some fifth copepodites were present in surface layers through the entire summer, and some younger copepodites persisted through the summer in progressively declining abundance just below the mixed layer. In autumn 1980 resurgence of early copepodite populations was rapid, occurring during the course of a prolonged October storm. The storm may have improved the habitat either by cooling the mixed layer or by resupplying nutrients to the euphotic zone.Eucalanus bungii reproduced in the mixed layer in early May and in early July. The first event was a spawning by females that had previously spawned in 1979 and then had returned to diapause. The second, heavier spawning (more females, more eggs per female) was by newly matured females from stocks that had overwintered as fifth copepodites. Nauplii peaked sharply in abundance on 19 July, one week after the peak in spawning. First and second copepodites peaked on 1 August, and all had advanced to the third copepodite stage by September. The diapause stock was established by September, principally between 250 and 500 m, and consisted of copepodite stages from third to sixth. Duration of the E. bungii life cycle appears to be typically two years. New nauplii develop as far as the third or fourth copepodite stage during their first summer, then enter diapause. The second summer they advance to the fifth copepodite stage and reenter diapause. Fifth copepodites mature in their third summer at two years of age. The males remain at depth and mate without subsequent feeding. Females migrate at night to the mixed layer where spawning occurs. About 20% of females that had already spawned in 1980 reentered diapause. They would reproduce again in their fourth summer at three years of age. All aspects of the life cycle suggest low mortality rates for copepodite stages, particularly at depth in the habitat occupied during diapuse. There can be no premium on rapid reproduction for E. bungii in the subartic Pacific, and there must even be benefit from spreading reproduction between years. This iteroparity may amount to a “bet-hedging” tactic, the young from a given mother having more than one chance to find sustaining conditions. It also produces gene flow between the year classes of the biennial life cycle.     

Salt marsh cliff stability in the oosterschelde

Salt marsh cliff erosion in the Oosterschelde, due to basal scour and small-scale failure, was monitored during a two-year period using reference stakes. The composite marsh cliffs have a cantilever profile. Their stability is evaluated from beam failure analysis. A model is proposed, in which the cantilever weight is taken as the motive force; the major resistive force is the tensile strength. By substituting height, undermining width and soil mechanical properties of the cliff in the model, one can identify the cliffs that are likely to fail. Salt marsh cliffs, which combine a large tensile strength due to roots at the top of the profile with a large compressive stress at the cliff base due to the sandy texture of the subsoil, display the highest resistance to beam failure. The critical cliff dimensions, observed in the field, correspond with the values calculated from the proposed model of beam failure.     

Modeling urban expansion by using variable weights logistic cellular automata: a case study of Nanjing,China

Simulation models based on cellular automata (CA) are widely used for understanding and simulating complex urban expansion process. Among these models, logistic CA (LCA) is commonly adopted. However, the performance of LCA models is often limited because the fixed coefficients obtained from binary logistic regression do not reflect the spatiotemporal heterogeneity of transition rules. Therefore, we propose a variable weights LCA (VW-LCA) model with dynamic transition rules. The regression coefficients in this VW-LCA model are based on VW by incorporating a genetic algorithm in a conventional LCA. The VW-LCA model and the conventional LCA model were both used to simulate urban expansion in Nanjing, China. The models were calibrated with data for the period 2000–2007 and validated for the period 2007–2013. The results showed that the VW-LCA model performed better than the LCA model in terms of both visual inspection and key indicators. For example, kappa, accuracy of urban land and figure of merit for the simulation results of 2013 increased by 3.26%, 2.96% and 4.44%, respectively. The VW-LCA model performs relatively better compared with other improved LCA models that are suggested in literature.     

The dependence of reflectance spectra of Mercury on surface terrain

Reflectance spectra of Mercury, covering the spectral range of ～0.3–1.1 μm obtained during 1963–1976, were examined for any correlations with surface terrain. Mercury's 6.1385°/day rotational rate, the phases of the planet around maximum elongations, and bidirectional reflectance spectroscopy theory were used to identify the surface area associated with each spectrum. Data from 1974–1975, re-reduced with improved standard star flux ratios, show a weak absorption band in the near infrared not see in earlier analyses. Older spectra suggest that the western longitudes of the unimaged side of Mercury are similar to the rest of the planet. Spectra of the intercrater plains in the 0–90° quadrant suggest a possible absorption band. Spectra of areas dominated by Caloris Basin with the encompassing smooth plains may show Fe²⁺ abundances in the soil comparable to lunar highlands soil. No striking differences between spectra of intercrater plains and spectra of smooth plains are found. The absorption features seen in spectra of Mercury are generally weaker than features seen in lunar spectra.