Variations in the dynamic response of structures founded on piles induced by obliquely incident SV waves

Although the seismic actions generally consist of a combination of waves, which propagates with an angle of incidence not necessarily vertical, the common practice when analyzing the dynamic behavior of pile groups is based on the assumption of vertically incident wave fields. The aim of this paper is to analyze how the angle of incidence of SV waves affects the dynamic response of pile foundations and piled structures. A three-dimensional boundary element-finite element coupling formulation is used to compute impedances and kinematic interaction factors corresponding to several configurations of vertical pile groups embedded in an isotropic homogeneous linear viscoelastic half-space. These results, which are provided in ready-to-use dimensionless graphs, are used to determine the effective dynamic properties of an equivalent single-degree-of-freedom oscillator that reproduces, within the range where the peak response occurs, the response of slender and nonslender superstructures through a procedure based on a substructuring model. Results are expressed in terms of effective flexible-base period and damping as well as maximum shear force at the base of the structure. The relevance and main trends observed in the influence of the wavefront angle of incidence on the dynamic behavior of the superstructure are inferred from the presented results. It is found that effective damping is significantly affected by the variations of the wave angle of incidence. Furthermore, it comes out that the vertical incidence is not always the worst-case scenario.     

Spatio-temporal variability of benthic macroalgae in a coral reef system highly influenced by fluvial discharge: Veracruz,Gulf of Mexico

The Veracruz Reef System, in the southern Gulf of Mexico, is a suitable area for the study of the temporal and spatial variability of macroalgae abundance, at reef settings influenced by the fluvial discharge of the Jamapa River, and by human activities in the city and port of Veracruz. With this purpose, the bottom cover of each morpho-functional group of benthic macroalgae (frondoses, turf, and crustose corallines), and hermatypic corals, was determined at ten selected coral reefs, on a seasonal basis (rainy and dry seasons), for the 2009–2015 period. The average cover of benthic macroalgae was high (53.1%), with turf as the dominant morpho-functional group (31.9%), as in several reef ecosystems in the tropical Atlantic, followed by crustose corallines (15.2%), and frondoses (6.1%). Although turf macroalgae is dominant, due to their high temporal and spatial variability, the Veracruz Reef System could not be considered to be in a stable state, but just in an intermediate unstable equilibrium state, which is highly influenced by a high sediment load. As expected, nearshore reefs presented higher macroalgae covers, and unexpectedly, the outer-shelf reefs presented the highest cover of frondoses. Despite fluvial discharge influence, no differences in cover were found between the rainy and dry seasons. There was a negative and significantly correlation between the cover of frondoses and turf, which suggests that the driver/s of the abundance of these macroalgae, act in opposite ways for each group. Three clusters of reefs, defined by community structure and conservation degree, were determined: nearshore or degraded, offshore or moderately conserved, and conserved; and the entire Veracruz Reef System is considered to be in a moderately state of conservation.     

Diffuse Component Spectra of Solar Active Regions at Submillimeter Wavelengths

Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200–1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2′ and 7′. These sizes agree with observed sizes of active regions at other wavelengths such as Hα and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6–2.9 × 10⁴ K, for source diameters of 2′–7′.     

Self-Similar and Self-Affine Properties of Two-Dimensional Fracture Patterns in Rocks

In this paper, we investigate the fractal properties of binary maps of rock fractures at different scales and different geological types, as well as different families of fracture patterns obtained from a two-dimensional Laplacian growth model (LGM). From these analyses we figure out which families of the LGM patterns match the structural properties of the fracture binary maps. The LGM is defined in terms of a nonlinear map that depends on two parameters, λ and \mathfraka\mathfrak{a}, that respectively define the area and shape of the elements of the aggregate that conforms the patterns. The fractal dimension and roughness exponent of the LGM patterns are found to depend on \mathfraka\mathfrak{a}, with 0 < \mathfrak a < 10<\mathfrak {a}<1. From a detailed statistical analysis of these patterns we found that the fractal dimensions of capacity, correlation and information decrease monotonically as \mathfraka\mathfrak{a} increases. We also found that the values of these three fractal dimensions tend to collapse on top of each other as \mathfraka\lessapprox1\mathfrak{a}\lessapprox1. Remarkably, the fractal properties of rock fractures in the scales from millimeters up to a few meters appear to be well represented by the fractal structure of the LGM families of patterns with \mathfraka=0.15\mathfrak{a}=0.15 and 0.30, while the fractal properties of rock fractures in the scale of kilometers seems to be well represented by the LGM family with \mathfraka=0.90\mathfrak{a}=0.90. In addition, the three fractal dimension values of fracture binary maps in the scales from millimeters up to meters were found to be different between them. Nonetheless, for fractures in the scale of kilometers, the values of the three fractal dimensions are very close to each other as an indication of self-similar behavior. Analysis of the corrections to the scaling of the roughness exponent, ζ, suggests that they are negligible for the LGM family of fracture patterns with \mathfraka=0.9\mathfrak{a}=0.9. This finding points to a self-affine structure for this family of patterns. In fact, the calculated roughness exponent results are in the range of values characteristic of rock fractures.     

Coral Ba/Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula,Mexico

The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/Ca_TC) and the Ca-substitutive fraction (Ba/Ca_CaF), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/Ca_TC (5.90 ± 0.56 μmol/mol) was ∼20% higher than Ba/Ca_CaF (4.85 ± 0.33 μmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/Ca_TC time-series is significant (r = 0.77, p < 0.05), allowing the use of the Ba/Ca_TC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/Ca_CaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater.     

Parent stars of extrasolar planets – VIII. Chemical abundances for 18 elements in 31 stars

We present the results of detailed spectroscopic abundance analyses for 18 elements in 31 nearby stars with planets (SWPs). The resulting abundances are combined with other similar studies of nearby SWPs and compared to a sample of nearby stars without detected planets. We find some evidence for abundance differences between these two samples for Al, Si and Ti. Some of our results are in conflict with a recent study of SWPs in the SPOCS data base. We encourage continued study of the abundance patterns of SWPs to resolve these discrepancies.     

GPS-derived Deformation of the Central Andes Including the 1995 Antofagasta Mw = 8.0 Earthquake

—In order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the Andes, a 215 site GPS network covering Chile and the western part of Argentina was selected, monumented and observed in 1993 and 1994. A dense part of the network in northern Chile and northwest Argentina, comprising some 70 sites, was re-observed after two years in October/November, 1995. The M _w = 8.0 Antofagasta (North Chile) earthquake of 30th July, 1995 took place between the two observations. The city of Antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench. Three different deformation processes have been considered for modeling the measured displacements (1) interseismic accumulation of elastic strain due to subduction coupling, (2) coseismic strain release during the Antofagasta earthquake and (3) crustal shortening in the Sub-Andes.¶Eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation. Assuming a uniform slip model of interseismic coupling, the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km. The geodetically derived fault plane parameters of the Antofagasta earthquake are consistent with results derived from wave-form modeling of seismolog ical data. The coseismic slip predicted by the variable slip model reaches values of 3.2 m in the dip-slip and 1.4 m in the strike-slip directions. The derived rake is 66°. Our geodetic results suggest that the oblique Nazca–South American plate convergence is accommodated by oblique earthquake slip with no slip partitioning. The observed displacements in the back-arc indicate a present-day crustal shortening rate of 3–4 mm/year which is significantly slower than the average of 10 mm/year experienced during the evolution of the Andean plateau.     

Contribution to the knowledge of the Domeyko Range in the Andes of Northern Chile

This work describes a geological scheme of the pre- And ean Domeyko Range of Northern Chile. This pre- And ean area consists of a basement formed by Paleozoic granitic, volcanic, and marine sedimentary rocks, and by Triassic acidic volcanics with continental intercalations. The Andean Basin developed in the Lias over the basement, with initial stages that include volcanic and continental sequences. A continuous marine environment existed in the Hettangian-Tithonian span, with volcanic events in the Bajocian, Callovian, Kimmeridgian, and Tithonian. Evaporitic facies developed in the Oxfordian-Kirnmeridgian. A marine-continental basin is recognized in the Neocomian, the Upper Cretaceous being represented by volcanic and continental deposits, a development similar to the Tertiary one; over these sequences volcanic, detrital, and saline deposits were laid down in the Plio-Pleistocene. Compressional tectonic cycles developed in the Upper Paleozoic, Upper Lias?, Upper Jurassic, Upper Cretaceous, and Tertiary, and tensional phases occured in the Triassic, Cretaceous, and Tertiary. The compressional stages were characterized by intrusive cycles while the tensional phases witnessed volcanic sedimentary events.     

From platform to basin to swell: orbital control on sedimentary sequences in the Oxfordian, Spain

Climatic, oceanographic and ecological changes that control the formation and deposition of sediment in shallow and deep depositional environments commonly occur with periodicities of a few 10 000 years. Consequently, in order to interpret sedimentary sequences in the geological past, high time resolution is required. This is best obtained by cyclostratigraphy. Three sections have been studied in the Oxfordian of north-eastern Spain: one represents a shallow, siliciclastic-carbonate platform with repetitive subaerial exposures, one an intraplatform basin with sponge bioherms, and one a swell where iron ooids and glauconite formed. The platform section displays a well-defined stacking pattern of depositional sequences; the deeper-water sections are well dated by ammonites. The correlation between the three sections is a best-fit solution integrating biostratigraphy, sequence stratigraphy and cyclostratigraphy. It is concluded that the small-scale depositional sequences formed in tune with the 100-ka orbital eccentricity cycle. An additional factor was differential subsidence that ruled basin morphology.