Sand waves and other bedforms in lower Cook Inlet,Alaska     

Arnold H. Bouma  Monty A. Hampton  Robert C. Orlando 《Marine Georesources & Geotechnology》2013,31(1-4):291-308

Abstract

Lower Cook Inlet in Alaska has high‐ tidal currents that average 3–4 knots and normally reach a peak of 6–8 knots. The bottom has an average depth of about 60–70 m in the central part of the inlet that deepens toward the south. Several types of bedforms, such as sand waves, dunes, ripples, sand ribbons, and lag deposits form a microtopography on the otherwise smooth seafloor. Each bedform type covers a small field, normally a few hundred to a few thousand meters wide, and usually several kilometers long parallel to the tidal flow. High‐resolution seismic systems, side‐scan sonar and bottom television were used to study these bedforms. Large sand waves with wavelengths over 300 m and wave heights up to 10 m were observed. Fields of ebb‐oriented or flood‐oriented asymmetric bedforms commonly grade into more symmetric shapes. Several orders of smaller sand waves and dunes cover the flanks of the very large bedforms. The crest directions of both size groups are normally parallel, but deviations of up to 90° have been observed; local deviations may occur where smaller forms approach the crests of the larger sand waves. Bottom television observations demonstrated active bedload transport in a northerly direction on crests and midflanks of southward asymmetric large sand waves, but not in their troughs. Movement of bedload occurs in the form of small ripples. Although the asymmetry of the large bedforms suggests that migration has taken place in the ebb or flood directions, the very low surface angles (2.5°‐8°) of these bedforms do not indicate regular movements. The large bedforms are probably relict features, or they migrate only under severe conditions, whereas active sand transport by ripples and smaller sand waves and dunes moves bedload back and forth with the tides. An understanding of such movements is essential for determining design criteria for offshore installations and in benthic‐faunal studies.  相似文献   

The use of egg shells to infer the historical presence of copepods in alpine lakes     

Roland Knapp  Jodi Garton  Orlando Sarnelle 《Journal of Paleolimnology》2001,25(4):539-543

Copepods (Class Crustacea, Order Copepoda) are rarely included in paleoecological studies of lakes because they lack long-lasting exoskeletal remains. We describe the remains of eggs (egg shells) from Hesperodiaptomus copepods that are well preserved and abundant in alpine lake sediments. We demonstrate that the egg shells are the remains of Hesperodiaptomus eggs based on (i) the similar size and morphology of egg shells collected from sediments and those produced from the hatching of eggs obtained from laboratory-maintained Hesperodiaptomus, and (ii) the finding that diapausing eggs collected from lake sediments and hatched in the laboratory produced copepod nauplii that were morphologically indistinguishable from those hatched from eggs produced by laboratory-maintained Hesperodiaptomus. Egg shells were approximately two orders of magnitude more abundant in sediment cores than were viable diapausing eggs, making egg shells superior to viable diapausing eggs for quantifying the historical presence and abundance of Hesperodiaptomus. These results have important implications for alpine lake restoration as egg shells can be used to identify lakes in which Hesperodiaptomus was eliminated by fish introductions but has failed to return after fish eradication, lakes in which the pre-disturbance conditions are likely to be restored only by reintroductions of this important taxon.  相似文献   

An ozone depletion event in the sub-arctic surface layer over Hudson Bay,Canada     

B. A. Ridley  T. Zeng  Y. Wang  E. L. Atlas  E. V. Browell  P. G. Hess  J. J. Orlando  K. Chance  A. Richter 《Journal of Atmospheric Chemistry》2007,57(3):255-280

During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) program, aircraft flights during April 7–11, 2000 revealed a large area air mass capped below ∼500 m altitude over Hudson Bay, Canada in which ozone was reduced from normal levels of 30–40 ppbv to as low as 0.5 ppbv. From some of the in-situ aircraft measurements, back-trajectory calculations, the tropospheric column of BrO derived from GOME satellite measurements, and results from a regional model, we conclude that the event did not originate from triggering of reactive halogen release in the sub-Arctic region of Hudson Bay but resulted from such an event occurring at higher latitudes over the islands of the northern Canada Archipelago and nearby Arctic Ocean with subsequent transport over a distance of 1,000–1,500 km to Hudson Bay. BrO _x remained active during this transport despite considerable changes in the conditions of the underlying surface suggesting that chemical recycling during transport dominated any local halogen input from the surface. If all of the tropospheric column density of BrO is distributed uniformly within the surface layer, then the mixing ratio of BrO derived from the satellite measurements is at least a factor of 2–3 larger than derived indirectly from in situ aircraft measurements of the NO/NO₂ ratio.  相似文献   

Detection and analysis of LNAPL using the instantaneous amplitude and frequency of ground‐penetrating radar data     

Luciana Orlando 《Geophysical Prospecting》2002,50(1):27-41

This paper reports the results of using the ground‐penetrating radar (GPR) method to detect light non‐aqueous phase liquids (LNAPL) floating on the water table in an area where the thickness of LNAPL present ranges from a few centimetres to several decimetres. To understand the GPR response in this context, GPR theoretical models are calculated using information from the literature and hydrogeological field data. The study revealed that in the case of LNAPL floating on the water table in a static condition, there is an increase in the reflection amplitude from the water table due to the decrease in the capillary fringe. Nevertheless the amplitude of reflection from the water table can discriminate the contaminated from the non‐contaminated zone. Apart from an analysis of the real traces, the analysis of some attributes of the complex trace, instantaneous amplitude, phase and frequency, are also good tools to detect hydrocarbons floating on the water table. Such attributes, depending on both the signal frequency and the hydrocarbon thickness, can also give information about the thickness of the hydrocarbon layer. It is concluded that analysing the lateral variations in signal amplitude of the real trace and in the amplitude, phase and instantaneous frequency of the complex signal permits the delimiting of the area polluted by the hydrocarbon.  相似文献   

Aspects geologiques et geophysiques des failles lithospheriques     

Orlando Vecchia 《International Journal of Earth Sciences》1957,46(1):50-69

Zusammenfassung An einigen Beispielen wird erläutert, da\ Störungszonen, welche die ganze Lithosphäre durchsetzen, eine Serie mehr oder minder ausgeprägter geologischer und geophysikalischer Erscheinungen zeigen. Diese erleichtern die Erkennung solcher Störungszonen auch in den Fällen, wo ihr Vorhandensein und ihre Narben an der Oberfläche durch tangentiale Druckeffekte einschlie\lich evtl. Gleittektonik oder auch durch Transgressionen verhüllt werden.

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Présenté à la Jahresversammlung 1956 der Geol. Vereinigung, Göttingen.  相似文献   

Using multicomponent GPR to monitor cracks in a historical building     

Luciana Orlando  Evert Slob   《Journal of Applied Geophysics》2009,67(4):327

We tested the usefulness of acquiring multicomponent GPR data to detect cracks in a historical building, and to monitor their dynamics, caused by a slowly and irregularly moving landslide. We used 2 GHz bipolar antennas in a configuration that allows for acquiring the in-line and cross-line electric field components with x- and y-directed antennas. The 2 × 2 data matrix was collected on a floor in the building along transects at four different times over a period of one year. The data were processed with a standard 2D scalar algorithm and with the latest 3D single component vector algorithm that corrects for antenna effects. We have implemented a 3D single component vector migration algorithm in a 2.5D sense to produce 2D slices of a 3D vector migration image by applying the algorithm on line data. This procedure allows for migrating single component line data taking into account all vector effects as well as three-dimensional wave propagation. We show that the 2.5D vector migration images have a much better in-line resolution than the migration images obtained by applying a standard 2D scalar migration algorithm.The GPR profiles agree with the a priori information about the structure of the floor. In particular, we detected two different types of anomalies, only a few of which can be due to utilities and to metallic mesh. Some shallower anomalies agree well with the cracks visible on the tiling, suggesting that some cracks can be directly detected using GPR. Visually there were no changes in the cracks on the floor and no clear changes in the GPR data could be attributed to possible subsurface changes in the cracks. The variations in the GPR images seemed primarily caused by changes in the coupling of the antennas with the investigated structure (floor) depending on the season when the measurements were made. For this reason the monitoring aspect of the survey is not successful.  相似文献   

Kinematic internal forces in deep foundations with inclined piles          下载免费PDF全文

Luis A. Padrón  Adrián Suárez  Juan J. Aznárez  Orlando Maeso 《地震工程与结构动力学》2015,44(12):2129-2135

This paper presents a parametric study that looks into the influence of pile rake angle on the kinematic internal forces of deep foundations with inclined piles. Envelopes of maximum kinematic bending moments, shear forces and axial loads are presented along single inclined piles and 2 × 2 symmetrical square pile groups with inclined elements subjected to an earthquake generated by vertically incident shear waves. Inclination angles from 0° to 30° are considered, and three different pile–soil stiffness ratios are studied. These results are obtained through a frequency–domain analysis using a boundary element–finite element code in which the soil is modelled by the boundary element method as a homogeneous, viscoelastic, unbounded region, and the piles are modelled by finite elements as Euler–Bernoulli beams. The rotational kinematic response of the pile foundations is shown to be a key factor on the evolution of the kinematic internal forces along the foundations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Fluid circulation and structural discontinuities inside Misti volcano (Peru) inferred from self-potential measurements     

Anthony Finizola  Jean-Franois Lnat  Orlando Macedo  Domingo Ramos  Jean-Claude Thouret  Francesco Sortino 《Journal of Volcanology and Geothermal Research》2004,135(4):216

One of the seven potentially active andesite stratovolcanoes in southern Peru, Misti (5822 m), located 17 km northeast and 3.5 km above Arequipa, represents a major threat to the population (900,000 inhabitants). Our recent geophysical and geochemical research comprises an extensive self-potential (SP) data set, an audio–magnetotelluric (AMT) profile across the volcano and CO₂ concentrations in the soil along a radial profile. The SP survey is the first of its kind in providing a complete mapping of a large andesitic stratovolcano 20 km in diameter. The SP mapping enables us to analyze the SP signature associated with a subduction-related active volcano.The general SP pattern of Misti is similar to that of most volcanoes with a hydrogeologic zone in the lower flanks and a hydrothermal zone in the upper central area. A quasi-systematic relationship exists between SP and elevation. Zones with constant SP/altitude gradients (Ce) are observed in both hydrogeologic (negative Ce) and hydrothermal (positive Ce) zones. Transition zones between the different Ce zones, which form a concentric pattern around the summit, have been interpreted in terms of lateral heterogeneities in the lithology. The highest amplitudes of SP anomalies seem to coincide with highly resistive zones. The hydrothermal system 6 km in diameter, which extends over an area much larger than the summit caldera, may be constrained by an older, concealed collapse caldera. A sealed zone has apparently developed through alteration in the hydrothermal system, blocking the migration of CO₂ upward. Significant CO₂ emanations are thus observed on the lower flanks but are absent above the hydrothermal zone.  相似文献   

The vibrational spectrum of calcite (CaCO<Subscript>3</Subscript>): an ab initio quantum-mechanical calculation     

M.?PrencipeEmail author  F.?Pascale  C. M.?Zicovich-Wilson  V. R.?Saunders  R.?Orlando  R.?Dovesi 《Physics and Chemistry of Minerals》2004,31(8):559-564

The vibrational spectrum of calcite (CaCO₃) is evaluated at an ab initio periodic quantum-mechanical level by using the CRYSTAL package. A localized basis set of Gaussian-type functions and the B3LYP hybrid Hamiltonian are adopted. The dynamical matrix is obtained by differentiating numerically the analytical first derivatives of the energy. The accuracy with respect to all computational parameters is documented. The calculated frequencies are compared with available IR and RAMAN data (16 and 5 peaks, respectively), the mean absolute error being less than 12 cm^–1 (frequencies range from 100 to 1600 cm^–1). Overall, the agreement with experiment is very satisfactory, and shows that simulation can produce at a relatively low cost the full spectra of crystalline compounds of mineralogical interest.  相似文献   

The destruction of mangroves     

Victor Canestri  Orlando Ruiz 《Marine pollution bulletin》1973,4(12):183-185

Coastal developments in Venezuela are leading to the rapid destruction of the mangrove forests. Population pressure leads to an overcrowding of public recreational beaches and the wealthy are increasingly seeking out previously deserted coasts. A rash of summer houses built on stilts over the shallow water is now extending around the mangrove areas, causing pollution, erosion and a progressive deterioration of the coastal environment.  相似文献