MM Herculis: An eclipsing binary of the RS CVn type

Differential photoelectric photometry inV, B, andU has been obtained for the eclipsing binary MM Her, a member of the RS Canum Venaticorum class. The light outside eclipse was Fourier-analyzed to study the wave. The migration and amplitude of the wave and the mean light level of the system now have been monitored from 1976 through 1980. The phase of wave minimum has decreased from 0 _. ^P 80 to 0 _. ^P 25, the wave amplitude has varied between 0 _. ^m 06 and 0 _. ^m 12, and the mean light level has fluctuated between 0.94 and 0.99. Observations within eclipse revealed that the eclipses are partial, not total as previously thought, and a new time of mid-eclipse was found to be JD (hel.)=2444 500.6665±0 _. ^d 0008. The Russell model was used to solve the 1980 light curve. Elements of the rectified light curve werei=86 _. ^° 35±0 _. ^° 09,r _h =0.070±0.002,r _c =0.125±0.001,L _h (V)=0.585±0.008 andL _h (B)=0.683±0.010. The geometric elements were forced on the pre-1980 light curves and found to be compatible. With these elements and previously obtained double-lined radial velocity curves, new absolute dimensions have been calculated: 1.18M and 1.58R for the hotter star and 1.27M and 2.83R for the cooler star. By plotting color indices on the color-color curve, spectral types of G2V and K21V were found, each uncertain by a couple of subclasses.Guest Observer Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.     

Buckling of a pervasively faulted lithosphere

We investigated the buckling response of a faulted elastic plate under horizontal compression using the finite element technique to better understand the effect of faults on the elastic behavior of a plate. We studied the effect of changes in fault spacing, depth and dip on the effective Young's modulus, buckling stress and wavelength. Our model consists of a thick elastic plate whose entire upper surface is cut by evenly spaced faults. We impose either an initial sinusoidal deformation with a fixed wavelength or a random deformation to the grid. A fault is represented as a free surface with no resolved shear stress and is allowed to slip in a specified direction using the method of slippery nodes. With the assumption of free slip on the faults, our model results represent an end member case in which the buckling wavelength and buckling stress are minimized by the presence of the faults.In our models, fault depth was varied from 0 to 75% of the plate thickness. As strain increases, the grid deforms by antisymmetric flexural folding and the initial imposed wavelength of deformation is modified such that the new buckling wavelength emerges. Our results show that the effective Young's modulus is a decreasing function of fault depth and an increasing function of fault spacing. In addition, buckling of the plate occurs at a lower stress for greater fault depths. Buckling wavelength is independent of the initial deformation wavelength however, it is modified by the presence of faults. For a plate with closely spaced faults extending through at least 75% of the plate, buckling occurs at a wavelength one half as large as that for a continuous plate. Buckling stress is not independent of the intial deformation wavelength, rather it increases slightly with increasing difference between the initial deformation wavelength and the buckling wavelength.Analytical models that approximate or ignore the effect of faulting can have large errors in calculation of the buckling stress. More importantly, modeling the observed wavelength of deformation in a faulted region with analytical solutions for continuous plates may result in a significant underestimate of elastic thickness. Fault dip does not strongly affect either the effective Young's modulus or the buckling wavelength. Thus, the buckling response should be the same for a plate cut by a low angle fault or a high angle fault.     

Localised strain in fissured clays: the combined effect of fissure orientation and confining pressure

Acta Geotechnica - This paper reports the main results of an experimental study on the mechanics of intensely fissured natural clays, extending our previous studies on scaly clay from Santa Croce...     

Rifting and pre‐rift lithosphere variability in the Orphan Basin,Newfoundland margin,Eastern Canada

The Orphan Basin, lying along the Newfoundland rifted continental margin, formed in Mesozoic time during the opening of the North Atlantic Ocean and the breakup of Iberia/Eurasia from North America. To investigate the evolution of the Orphan Basin and the factors that governed its formation, we (i) analysed the stratigraphic and crustal architecture documented by seismic data (courtesy of TGS), (ii) quantified the tectonic and thermal subsidence along a constructed geological transect, and (iii) used forward numerical modelling to understand the state of the pre‐rift lithosphere and the distribution of deformation during rifting. Our study shows that the pre‐rift lithosphere was 200‐km thick and rheologically strong (150‐km‐thick elastic plate) prior to rifting. It also indicates that extension in the Orphan Basin occurred in three distinct phases during the Jurassic, the Early Cretaceous and the Late Cretaceous. Each rifting phase is characterized by a specific crustal and subcrustal thinning configuration. Crustal deformation initiated in the eastern part of the basin during the Jurassic and migrated to the west during the Cretaceous. It was coupled with a subcrustal thinning which was reduced underneath the eastern domain and very intense in the western domains of the basin. The spatial and temporal distribution of thinning and the evolution of the lithosphere rheology through time controlled the tectonic, stratigraphic and crustal architecture that we observe today in the Orphan Basin.     

Measurement of the sortable silt current speed proxy using the Sedigraph 5100 and Coulter Multisizer IIe: precision and accuracy

The weight percentage and mean size of the 10–63 μm terrigenous silt fraction (termed 'sortable silt') of fine-grained marine sediments have recently been argued to be proxies for near-bottom palaeocurrent intensity. This paper details the accuracy and precision of the Sedigraph 5100 and the Coulter Multisizer IIe in determining the weight percentage and mean size of the sortable silt at abundances characteristic of deep-ocean sediments. Three sortable silt standards and a fine silt/clay diluent were generated from natural deep-sea sediment of the Iceland Basin. These were used to produce silty clays with standard additions of sortable silt ranging from 1% to 20% of the total by weight. Accuracy was measured relative to the size of the pure spike measured by each instrument. At sortable silt abundance >5%, the Sedigraph and the Coulter Multisizer estimate both weight percentage and mean grain size precisely and accurately, while below 5%, instrumental noise degrades their performance. On the basis of the Sedigraph results, a series of percentage errors is defined, which may be applied to sortable silt mean size and weight percentage estimates used in palaeoceanographic near-bottom current reconstruction. It is suggested that, ideally, palaeocurrent reconstructions should be based on Sedigraph determinations of the 0–63 μm grain size distribution, yielding both mean and abundance, or on Coulter Multisizer determinations of the sortable silt grain size mean. The Coulter Multisizer may prove especially useful in regions of very depleted (<5%) sortable silt component.     

Simultaneous photometry and spectroscopy of the newly discovered γ Doradus variable HR 8330=HD 207223

We present BV photometry and simultaneous high-resolution, high signal-to-noise ratio spectroscopy of the newly-discovered γ Doradus variable HR 8330 taken during the 1997 and 1998 observing seasons. We calculate power spectra for the B - and V -band data sets and for the time series defined throughout the observing season at each point across the Fe  ii λ 4508.289 and the Ti  ii λ 4501.278 line profiles to search for periodic variability. Period analysis reveals a single, 2.6-d period in both the photometric and the spectroscopic data, with a 237° phase lag between them. Based on the location of HR 8330 in the HR diagram and the characteristics of its photometric and spectroscopic variations, we conclude that HR  8330 is a bona fide γ Doradus-type pulsating variable.     

Assessment of Offshore New Jersey Sources of Beach Replenishment Sand by Diversified Application of Geologic and Geophysical Methods

Beach replenishment serves the dual purpose of maintaining a source of tourism and recreation while protecting life and property. For New Jersey, sources for beach sand supply are increasingly found offshore. To meet present and future needs, geologic and geophysical techniques can be used to improve the identification, volume estimation, and determination of suitability, thereby making the mining and manag ing of this resource more effective. Current research has improved both data collection and interpretation of seismic surveys and vibracore analysis for projects investigating sand ridges offshore of New Jersey. The New Jersey Geological Survey in cooperation with Rutgers University is evaluating the capabilities of digital seismic data (in addition to analog data) to analyze sand ridges. The printing density of analog systems limits the dynamic range to about 24 dB. Digital acquisition systems with dynamic ranges above 100 dB can permit enhanced seismic profiles by trace static correction, deconvolution, automatic gain scaling, horizontal stacking and digital filtering. Problems common to analog data, such as wave-motion effects of surface sources, water-bottom reverberation, and bubble-pulse-width can be addressed by processing. More than 160 line miles of digital high-resolution continuous profiling seismic data have been collected at sand ridges off Avalon, Beach Haven, and Barnegat Inlet. Digital multichannel data collection has recently been employed to map sand resources within the Port of New York New Jersey expanded dredge-spoil site located 3 mi offshore of Sandy Hook, New Jersey. Multichannel data processing can reduce multiples, improve signal-to-noise calculations, enable source deconvolution, and generate sediment acoustic velocities and acoustic impedance analysis. Synthetic seismograms based on empirical relationships among grain size distribution, density, and velocity from vibracores are used to calculate proxy values for density and velocity. The seismograms are then correlated to the digital seismic profile to confirm reflected events. They are particularly useful where individual reflection events cannot be detected but a waveform generated by several thin lithologic units can be recognized. Progress in application of geologic and geophysical methods provides advan tages in detailed sediment analysis and volumetric estimation of offshore sand ridges. New techniques for current and ongoing beach replenishment projects not only expand our knowledge of the geologic processes involved in sand ridge origin and development, but also improve our assessment of these valuable resources. These reconnaissance studies provide extensive data to the engineer regarding the suitability and quantity of sand and can optimize placement and analysis of vibracore samples.     

Geomechanical simulation to predict open subsurface fractures

Geomechanical simulation of the evolution of a geological structure can play an important role in predicting open fracture development for all stages in that structure's development. In this work, three such geomechanical simulations are used to predict the evolving stress and strain fields, including dilational and compactional changes in the rock fabric in developing fault and fold systems. Their consequences for open fracture development and flow are addressed. These simulated stress and strain fields show considerable spatial and temporal heterogeneity that is consistent with deformation patterns observed in both natural examples and in laboratory-deformed analogues. But the stress and strain states that develop are neither co-axial nor do they bear a simple relationship to one another. The dilational and compactional strains, manifest as open fracturing or sealing, represent some significantly increased or significantly decreased flow rates. However, open-fracture predictions based on such geomechanical simulations are extremely difficult to validate with any degree of confidence as there is little direct evidence of sub-surface fracture distributions. In this context we also discuss possible integration of seismic anisotropy measurements, as an independent measure of open fracture alignment, to support the geomechanically derived fracture predictions. The focus of this work is on volumetric strains in fault zone evolution, though folding is also addressed.     

The plinian fallout associated with Quilotoa's 800 yr BP eruption,Ecuadorian Andes

Large volcanic eruptions at dacitic or rhyolitic volcanoes often generate exceptional volumes of fine ash that mantles an area up to a million km². These eruptions are characterized by extreme fragmentation of the magma and hence extraordinary dispersal of ash and are categorized as plinian, ultraplinian, or phreatoplinian events. Large-volume co-ignimbrites or co-plinian ashes are often produced by such eruptions. High fragmentation indices of > 90% are attributed to the violent eruption of silicic magma, especially if augmented by fuel-coolant reactions produced when abundant external water interacts with the magma. The present study documents a case where the fine ash (≤ 1 mm diameter) fall deposit related to the plinian phase of the eruption comprises the overwhelming bulk – about 87 wt.% of the eruptive products. This is another example demonstrating the predominance of a widespread, fine-grained, co-plinian ash which follows the initial coarser lapilli fall. Historical eruptions at two other Andean volcanoes Quizapu, (Chile) and Huaynaputina, (Peru), and at Santa Maria, (Guatemala) and Novarupta, (Alaska) produced similar ash fall sequences.     

Pre-eruptive physical conditions of El Reventador volcano (Ecuador) inferred from the petrology of the 2002 and 2004–05 eruptions

A petrological study of the eruptive products of El Reventador allowed us to infer the magmatic processes related to the 2002 and 2004–05 eruptions of this andesitic stratovolcano. On November 3, 2002, El Reventador experienced a highly explosive event, which was followed by emplacement of two lava flows in November–December 2002. Silica contents range from 62 to 58 wt.% SiO₂ for the November 3 pyroclastic deposits to 58–56 and 54–53 wt.% SiO₂ for the successive lava flows. In November 2004 eruptive activity resumed supplying four new lava flows (56–54 wt.% SiO₂) between November 2004 and August 2005.