Slope Anomalies Research Articles

Safety assessment in dams due to downstream slope anomalies

Recent cases of tailings dam failure in Brazil have demonstrated in the current methods of safety assessment of these structures. One of the most employed methods is the evaluation through routine inspections and audits, but this method is considered non-deterministic and affected by the expertise of the evaluator. This paper presents the results of numerical simulations of anomalies commonly found in safety inspections to measure the impact of these anomalies on the dam safety factor. The study was limited to numerical simulations of five types of dams (three downstream and two upstream dams), with varying embankment and tailings strength parameters, simulating different magnitudes of downstream slope anomalies (cracks, scour, and resurgence), totaling a sample space of 270 analyses. The results show that there were average reductions in safety ranging from 4% to 10% for scour simulations, 8% to 25% for resurgence, and 9% to 24% for cracking. The sample standard deviation of the analyses ranged from 8 to 12%. It was also observed that the combined effect of the anomalies showed proportional overlapping effects in reducing the range of safety. It was concluded that the simulated failures are important variables to be evaluated in inspections, not only for demonstrate deviations in the operation and maintenance of structures, but also to predict the magnitude of these failures in dam designs.

The Role of Planetary-Scale Eddies on the Recent Isentropic Slope Trend during Boreal Winter

AbstractAccording to baroclinic adjustment theory, the isentropic slope maintains its marginal state for baroclinic instability. However, the recent trend of Arctic warming raises the possibility that there could have been a systematic change in the extratropical isentropic slope. In this study, global reanalysis data are used to investigate this possibility. The result shows that tropospheric isentropes north of 50°N have been flattening significantly during winter for the recent 25 years. This trend pattern fluctuates at intraseasonal time scales. An examination of the temporal evolution indicates that it is the planetary-scale (zonal wavenumbers-1–3) eddy heat fluxes, not the synoptic-scale eddy heat fluxes, that flatten the isentropes; synoptic-scale eddy heat fluxes instead respond to the subsequent changes in isentropic slope. This extratropical planetary-scale wave growth is preceded by an enhanced zonal asymmetry of tropical heating and poleward wave activity vectors. A numerical model is used to test if the observed latent heating can generate the observed isentropic slope anomalies. The result shows that the tropical heating indeed contributes to the isentropic slope trend. The agreement between the model solution and the observation improves substantially if extratropical latent heating is also included in the forcing. The model temperature response shows a pattern resembling the warm-Arctic–cold-continent pattern. From these results, it is concluded that the recent flattening trend of isentropic slope north of 50°N is mostly caused by planetary-scale eddy activities generated from latent heating, and that this change is accompanied by a warm-Arctic–cold-continent pattern that permeates the entire troposphere.

Investigation of the structural, magnetic, impedance properties in samarium-doped yttrium iron garnet

Y3-xSmxFe5O12 (x = 0, 1, 2, 3) ferrites with pure single phase were prepared by sol-gel method. The effects of Sm3+-substitution on crystal structure and magnetic properties were systematically investigated. The Sm3+ ions substitution in Y3+ sites resulted in lattice expansion and structural distortion by changing Fe[a]-O-Fe(d) bond length and bond angle, which further modified the magnetization properties and led to the decrease of saturation magnetization by regulating super-exchange interaction between tetrahedron and octahedron sites. The relationships between complex impedance with frequency and temperature were studied, suggesting that asymmetric and depressed semicircle spectrum is owing to a non-Debye like relaxation process controlled by thermal vibration charge carriers, and the electrical conduction within grains is dominated by the charge carrier transition between Fe3+ and Fe2+ sites due to the ionization effect of oxygen vacancies. By fitting the equivalent circuits, it was found that grain boundary and grain have different contributions to complex impedance spectrum while grain boundary relaxation play the dominant role at higher temperature. The slope anomalies of relaxation frequency and conductivity were observed near the ferromagnetic transition temperature (TC) owing to the magneto-electric coupling effect, revealing that magnetic ordering has a great influence on electrical conduction. Ac conductivity analysis reveal that the main conduction mode experiences a gradual transition from a small polaron hopping model (T < 550K) to an overlapping large polaron tunneling model (T > 550K). Moreover, the increase in conductivity is ascribed to two factors: the thermally assisted charge carrier hopping and the ionization effect of oxygen vacancy due to the incorporation of Sm ions.

Subtidal variability in the Taiwan Strait induced by combined forcing of winter monsoon and topography

As an important channel connecting the East and South China Seas, circulations in the Taiwan Strait are strongly influenced by the East Asian monsoon and the topography of the strait, especially the Taiwan Bank (TWB), which is a remarkable topographic feature located at the southern entrance to the strait. Based on a series of pressure gauges deployed roughly 40 km offshore along the western Strait, subtidal sea-level variability under the combined impact of winter monsoon and topography was studied. The analyses show significant along-strait coherences of subtidal sea levels and their coherences with the large-scale monsoon wind for periods from 2 to 14 days. It is suggested that these fluctuations are mainly forced waves driven by the large-scale winds. In addition to the normal cross-shore wind setup, a sea-level setup in the along-strait direction is confirmed, which is induced by the combined forcing of the fluctuating winter monsoon and the blocking of the TWB. A southward current surge driven by a northerly wind event will cause a rising sea level over the TWB inducing a southward along-shore slope anomaly to the north of the TWB and a reversed slope anomaly to the south. The subtidal current through the channel to the west of the TWB is found to be influenced by the reversed slope anomalies generated via the along-shore setup.

Remote Sensing of CDOM, CDOM Spectral Slope, and Dissolved Organic Carbon in the Global Ocean.

A Global Ocean Carbon Algorithm Database (GOCAD) has been developed from over 500 oceanographic field campaigns conducted worldwide over the past 30 years including in situ reflectances and coincident satellite imagery, multi- and hyperspectral Chromophoric Dissolved Organic Matter (CDOM) absorption coefficients from 245–715 nm, CDOM spectral slopes in eight visible and ultraviolet wavebands, dissolved and particulate organic carbon (DOC and POC, respectively), and inherent optical, physical, and biogeochemical properties. From field optical and radiometric data and satellite measurements, several semi-analytical, empirical, and machine learning algorithms for retrieving global DOC, CDOM, and CDOM slope were developed, optimized for global retrieval, and validated. Global climatologies of satellite-retrieved CDOM absorption coefficient and spectral slope based on the most robust of these algorithms lag seasonal patterns of phytoplankton biomass belying Case 1 assumptions, and track terrestrial runoff on ocean basin scales. Variability in satellite retrievals of CDOM absorption and spectral slope anomalies are tightly coupled to changes in atmospheric and oceanographic conditions associated with El Niño Southern Oscillation (ENSO), strongly covary with the multivariate ENSO index in a large region of the tropical Pacific, and provide insights into the potential evolution and feedbacks related to sea surface dissolved carbon in a warming climate. Further validation of the DOC algorithm developed here is warranted to better characterize its limitations, particularly in mid-ocean gyres and the southern oceans.

SPATIAL DISTRIBUTION OF THE SNOW ACCUMULATION RATE ALONG THE ICE FLOW LINES BETWEEN RIDGE B AND LAKE VOSTOK

During the 45 th –57 th Russian Antarctic Expeditions (1999–2012) an intensive program of glaciological and geophysical observations have been carried out in the region between the subglacial Lake Vostok and the Ridge B, Сentral Antarctica. In this work we present the instrumentally obtained snow accumulation data along the northern ( NVFL ) and southern ( VFL ) ice flow lines passing through the Lake Vostok. The mean accumulation rate at the NVFL and VFL profiles is 29–37 kg m -2 yr -1 and 21–24 kg m -2 yr -1 , respectively. Thus, this region is characterized by a strong latitudinal gradient of the snow accumulation rate, while the longitudinal one is an order of magnitude less. The spatial distribution of the accumulation rate along the VFL is characterized by a sharp variability attributed to the snow re-deposition due to the wind interplay with the local glacier surface slope anomalies. The new data on the stable water isotope concentration ( 18 O) along the VFL profile are also presented.

An Internet-Enabled Wireless Multi-Sensor System for Continuous Monitoring of Landslide Processes

Monitoring and early warning systems, although being capable of continuously collecting field data related to landslide processes, are usually unable to autonomously detect and analyze signs of landslides in real time. This paper presents the design and experimental implementation of an autonomous landslide monitoring system. Besides reliably issuing early warnings in case of detected slope anomalies, the monitoring system is primarily designed to support human individuals in assessing the risk of landslide and to improve the understanding of the slope behavior, which may help to reduce economic losses and fatalities caused by landslides. Specifically, intelligent wireless sensor nodes are distributed in the observed slope to autonomously collect, analyze and communicate relevant environmental parameters in real time. Supporting remote analyses of the collected field data, a web application, which is installed on a computer connected to the on-site sensor nodes, enables an automated dissemination of slope parameters through the Internet. Last but not least, geospatial information stemming from external sources is integrated into the monitoring system to provide a comprehensive overview of landslide-related slope conditions.

Nuclear temperatures from evaporation fragment spectra and observed anomalies

The extreme back-angle evaporation spectra of alpha, lithium, beryllium, boron and carbon from different compound nuclei near A=100 (EX=76-210 MeV) have been compared with the predictions of standard statistical model codes such as 'CASCADE' and 'GEMINI'. It was found that the shapes of the alpha spectra agree well with the predictions of the statistical models. However the spectra of lithium, beryllium, boron and carbon show significantly gentler slopes implying higher temperature of the residual nuclei, even though the spectra satisfy all other empirical criteria of statistical emissions. The observed slope anomaly was found to be largest for lithium and decreases at higher excitation energy. These results could not be understood by adjusting the parameters of the statistical models or from reaction dynamics and might require examining the statistical model from a quantum mechanical perspective.

Interannual Tropical Pacific Sea Surface Temperatures and Their Relation to Preceding Sea Level Pressures in the NCAR CCSM2

Abstract This paper describes aspects of tropical interannual ocean/atmosphere variability in the NCAR Community Climate System Model Version 2.0 (CCSM2). The CCSM2 tropical Pacific Ocean/atmosphere system exhibits much stronger biennial variability than is observed. However, a canonical correlation analysis technique decomposes the simulated boreal winter tropical Pacific sea surface temperature (SST) variability into two modes, both of which are related to atmospheric variability during the preceding boreal winter. The first mode of ocean/atmosphere variability is related to the strong biennial oscillation in which La Niña–related sea level pressure (SLP) conditions precede El Niño–like SST conditions the following winter. The second mode of variability indicates that boreal winter tropical Pacific SST anomalies can also be initiated by SLP anomalies over the subtropical central and eastern North Pacific 12 months earlier. The evolution of both modes is characterized by recharge/discharge within the equatorial subsurface temperature field. For the first mode of variability, this recharge/discharge produces a lag between the basin-average equatorial Pacific isotherm depth anomalies and the isotherm–slope anomalies, equatorial SSTs, and wind stress fields. Significant anomalies are present up to a year before the boreal winter SLP variations and two years prior to the boreal winter ENSO-like events. For the second canonical factor pattern, the recharge/discharge mechanism is induced concurrent with the boreal winter SLP pattern approximately one year prior to the ENSO-like events, when isotherms initially deepen and change their slope across the basin. A rapid deepening of the isotherms in the eastern equatorial Pacific and a warming of the overlying SST anomalies then occurs during the subsequent 12 months.

TOPEX/Poseidon and Jason Equatorial Sea Surface Slope Anomaly in the Atlantic in 2002: Comparison with Wind and Current Measurements at 23W

A time series of velocity profile in the upper 150 m of the equatorial Atlantic was gathered at 23W in 2002 within the PIRATA program. It constitutes the first time series of near surface current measurements simultaneous with altimetric data in the equatorial Atlantic. The surface slope anomaly along the equator is computed from satellite altimetry, and, as a proxy for the pressure gradient along the equator, compared with the wind and near surface current data. In a first step, a time series of the surface slope anomaly along the equator in the Atlantic is computed from the 10-year-long TOPEX/Poseidon sea level anomalies. A sensitivity study establishes the robustness of the calculation. Apart from a 15 cm bias, the equatorial sea surface slope anomalies estimated either from TOPEX/Poseidon or from Jason over the 6-month overlap (Feb.–Aug. 2002) do not reveal drastic differences. We produce two sea surface slope anomaly composite time series for 2002 (one with T/P data, the other with Jason data during the commissioning phase) and compare them to the wind and velocity data at 23W. As expected, the near surface velocity and depth of the upper limit of the equatorial undercurrent (EUC) are extremely well correlated with the surface pressure gradient anomaly. 10-year-long time series of altimetry-derived zonal sea surface slope anomaly and ECMWF ERA40 wind stress are also well correlated. They exhibit similar spectral content and similar anomalous years. This is a first step towards a full analysis of the EUC dynamics using altimetry, PIRATA data (near surface current and subsurface thermohaline structure) and model. These initial comparisons reinforce the utility of Jason measurements for continuing the 10-year and highly accurate TOPEX/Poseidon time series for study of equatorial signals.

Structural development of the Jurassic Magnetic Quiet Zone off Morocco and identification of Middle Jurassic magnetic lineations

Geophysical investigations carried out during two Meteor cruises have revealed weak linear magnetic anomalies in those parts of the Jurassic Magnetic Quiet Zone (JMQZ) off Morocco that are not affected by Cenozoic igneous activity. The linear magnetic anomalies are not correlated with variations in relief or structure of oceanic crust. Using the reversal sequence M25‐M41, the anomalies of the JMQZ can be modeled with a half spreading rate of 2.2 cm/yr. Extrapolation of the weak lineations back to the slope anomaly S1 results in a breakup age of 170 Ma. According to this interpretation the crust of the JMQZ off Morocco has formed during the time 170–155 Ma (Bajocian to Oxfordian). However, much lower spreading rates (around 1 cm/yr) cannot be excluded. S1 coincides with a poorly developed “seaward dipping reflector sequence” (SDRS), which is most likely its source. The SDRS corroborates the earlier claim that S1 marks the ocean‐continent transition. Seaward of S1 is a 70‐km‐wide strip of horizontal reflectors that become landward dipping to the west in the uppermost part of the basement; it parallels S1 over a distance of 200 km and may indicate excessive magma supply within the first 2 m.y. of seafloor spreading. Similar landward dipping reflectors are observed also in the conjugate Sohm Abyssal Plain off Nova Scotia. The average magnetization of the landward dipping reflectors is much lower than that of the SDRS. A lower crustal body with a seismic velocity of ∼7.3 km/s, which formed during the Neogene beneath the eastern part of the Essaouira Rise, has only a weak magnetization (&lt;0.5 A/m).

Utopia Basin, Mars: Characterization of topography and morphology and assessment of the origin and evolution of basin internal structure

Recently obtained Mars Orbiter Laser Altimeter (MOLA) topography has permitted a new assessment of the morphology, structure, and history of Utopia Planitia. The new topographic data convincingly demonstrate that the Utopia region is an impact basin, as originally proposed byMcGill[1989], whose major topographic expression is a circular, 1–3 km deep depression ∼3200 km in diameter. Utopia Basin is the largest easily recognizable impact structure in the northern hemisphere of Mars and is the only portion of the northern lowlands that exhibits a distinct large‐scale impact signature; its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the Noachian period. Using slope maps derived from gridded topography, we have mapped a series of linear slope anomalies within the basin and have analyzed their origin. These features can be classified into two groups: one oriented dominantly radial to the basin and the other oriented dominantly circumferential. The circumferential features are tens of kilometers wide and hundreds of kilometers long and appear to remain relatively constant with respect to elevation. We explore end‐member hypotheses (1) that the features formed by the direct action of water/ice or (2) that they are tectonic wrinkle ridges. We interpret the majority of these features to be due to tectonic deformation (primarily wrinkle‐ridge formation), modified by later sedimentation associated with the emplacement of the outflow channels and the formation of the Vastitas Borealis Formation. On the basis of the characteristics of these features and their association with polygonal terrain, thumbprint terrain, smoothness of units, and evidence of sedimentary deposits, we find that our results support earlier hypotheses proposing that a significant volume of water occupied Utopia Basin during the late Hesperian period of outflow channel formation. Utopia Basin differs significantly in depth and degradation state from the deeper and fresher‐appearing Hellas Basin, although the two are both Noachian in age. A significant part of this difference seems reasonably interpreted to be the result of the extensive sedimentary and volcanic infilling history of the northern lowlands.

Semiclassical description of transfer reactions at near-barrier energies for the systems

Abstract Transfer reactions at four near-barrier energies for the systems 32 S + 102,104 Ru were studied. The differential cross sections of the strong transfer channels were measured with an experimental set-up yielding good mass number, nuclear charge and energy resolution. With a semiclassical coupled channel model the measured transfer cross sections were analyzed and transfer form factors were extracted. At energies even slightly above the Coulomb barrier, “slope anomalies” were observed. If the reasons for slope anomalies are not taken into account, the determination of transfer form factors out of such measurements can be incorrect. It is shown in this paper how such a wrong determination of form factors can be avoided even when slope anomalies occur. With the help of the extracted transfer form factors fusion excitation functions and barrier distributions of the systems 32 S + 102,104 Ru were calculated. This proves that transfer channels play an important role in sub-barrier fusion processes for the studied systems.

Susceptibility and koenigsberger ratio of the oceanic crust deduced from magnetic reversals southeast of the Agulhas Bank

The Cape Slope Anomaly marks the contact between mid-Cretaceous oceanic crust and the southeastern edge of the Agulhas Bank, which is composed of weakly magnetic continental crust. Amplitude changes in the Cape Slope Anomaly reflect reversals in the direction of remanent magnetization with the oceanic crust. However, the consistent shape of the Cape Slope Anomaly indicates that the anomaly is dominated by “induced” magnetization (which may include a component of viscous remanent magnetization indistinguishable in effect from true induced magnetization). This observation supports the interpretation of the anomaly bounding the oceanic crust off the west coast of South Africa as a product of contact geometry, and not the result of a magnetic reversal. Similarly, other magnetic anomalies along the boundaries between continental and oceanic crust may be largely due to contact geometry.

The Transmission from Rifting to Seafloor Spreading: Magnetic Slope off Morocco

In many cases, passive continental margins are paralleled by a prominent magnetic anomaly, the so-called 'slope anomaly'. Off the Atlantic coast of Morocco, the slope anomaly (named SI) varies considerably along the strike in amplitude and shape (Fig. 1). The variations are correlated to changes in the magnctic character or the subsided and fractured continental crust eastward of the slope anomaly where lineated magnetic anomalies, nearly parallel to S1, were observed. Seaward of S1 the anomalies are generally much weaker. They are also parallel to the slope anomaly, however less continuous.

Oceanic crust next to passive margins: A structural origin for magnetic zones

Sea-surface 3-D magnetic intensity and resolution threshold curves have been completed for various patterns of spreading-generated magnetic source blocks on the sea-floor. These curves confirm that the earliest magnetic anomaly source blocks to form between oblique-to-spreading continental margins are too small to be individually resolved at the sea surface. This result suggests that a magnetically bland area (quiet zone) will develop during the early stages of spreading between oblique margins, regardless of the behaviour of the Earth's magnetic field at the time that the sea-floor formed. Sea-surface 3-D magnetic anomaly patterns have been computed for a possible sea floor spreading pattern formed between oblique-to-spreading continental margins during a time when regular magnetic reversals were occurring. This computation not only generates both the slope anomalies and quiet zones that characterize such margins, but also generates a diagnostic set of notched and bifurcated anomaly pattern elements, which we have subsequently recognized in marginal magnetic quiet zones adjacent to eastern Canada.

The East Coast Magnetic Anomaly

A model is proposed for the East Coast Magnetic Anomaly that, for the first time, incorporates an observed basement feature-a normal fault that consistently lies below the landward flank of the anomaly. The East Coast Magnetic Anomaly is similar to slope anomalies found over passive continental margins in many parts of the world. Thus the proposed model can be used to interpret slope anomalies in general.

Magnetic smooth zones and slope anomalies: a mechanism to explain both

Marginal magnetic smooth zones occur only along continental margins where these are oblique (not normal) to the regional fracture-zone trend. This relationship suggests a simple geometric mechanism which can generate marginal smooth zones and abyssal smooth zones during times of typical reversal history. The mechanism provides an explanation of “slope anomalies” and other smooth-zone characteristics, and casts doubt on the validity of using smooth zones as evidence for long fixed polarity intervals.

Magnetic anomalies associated with the southeastern continental margin of South Africa

A total magnetic intensity, iso-magnetic map is presented and discussed. Between East London and Durban large east-west trending anomalies are known on land and can be traced onto the continental shelf but not beyond the slope. Elsewhere the continental shelf is characterized by a remarkably quiet magnetic field. A feature of the map is the linear anomaly, named the Cape Slope Anomaly, which is parallel to the continental margin and coincides approximately with the 68° small circle about the early pole of opening for the South Atlantic as given by Le Pichon and Hayes (1971). The anomaly is traced between 30°54′S, 30°48′E and 37°45′S, 20°31′E and is interpreted as occurring over the truncated edge of a semi-infinite, sub-horizontal, remanently magnetized plate in oceanic crust beyond the continental margin. Between 37°03′S, 21°49′E and 37°41′S, 21°12′E the Slope Anomaly occurs over a ridge named the Agulhas Ridge. A continuous seismic reflection profile over the ridge shows acoustic basement occurring under a cover of sediments. A two dimensional model study indicates that the basement materials may belong to the body causing the anomaly with the exception of the basement material that forms the landward peak of the ridge, which is non-magnetic.

Geophysical study of the northwest African margin off Morocco

Six geophysical profiles were taken over the northwestern African margin between the Canary Islands and Morocco. A magnetic smooth zone occupies the upper continental rise landward of lineated sea-floor spreading anomalies of Late Jurassic to Early Cretaceous age. This smooth zone is believed due in part to a Late Jurassic uniform polarity interval; its seaward boundary is correlated with a basement high and/or abrupt landward thickening of sediments. Spreading may have started over 200 × 10 6 yr ago at a rate of 0·55 cm/yr and accelerated 150 to 160 × 10 6 yr at the smooth zone boundary. No counterpart of the east coast magnetic slope anomaly was observed off Morocco while the distance between the shelf break and the smooth zone boundary is also less here than off northeastern America. This difference suggests a shift in the position of the accreting plate boundary from west to east, about 200 × 10 6 yr ago, after the formation of the slope anomaly. Gravity data show that the Moroccan margin is largely in isostatic equilibrium, and that the zone of transition from oceanic to continental crustal thickness is wider off the Canaries (400 km) than off Morocco (100–150 km). The sediment section of the seismic reflection profiles includes an upper acoustically transparent unit (usually restricted to the upper rise) a middle stratified unit, and a lower transparent unit. The upper unit is probably pelagic calcareous ooze. Other lithologies are unknown but the stratified unit may in part include an Early Tertiary unconformity. Sections of the shelf and slope exhibit deformation that have probably been caused by the Alpine orogeny.