Determination of depth to the magnetic sources using spectral analysis with application to Sicily, Southern Italy

2020 ◽  
Author(s):  
Yemane Kelemework ◽  
Maurizio Fedi
Keyword(s):  
Spectral Analysis ◽  
Critical Evaluation ◽  
Power Spectra ◽  
Window Size ◽  
Depth Estimation ◽  
Careful Consideration ◽  
Source Distribution ◽  
Distribution Models ◽  
Theoretical Frameworks ◽  
Potential Field Data

<p>Spectral analysis is among the most old and common techniques for the processing and interpretation of potential field data. This is related to the decay properties of the field power spectra which allows an easy estimation of the depths to the top and to the bottom of the sources of magnetic and gravity field anomalies. Such analysis can be accomplished however in different theoretical frameworks, assuming either a statistical ensemble of homogeneous sources or random fractal source distribution. Here, we present the many existing spectral analysis techniques to compare them with respect to estimating the depth to the source top and bottom. We evidence practical constraints on the depth estimation and inherent assumptions/limitations of the different approaches. Depth estimation using spectral methods requires a critical evaluation of window size, window location, and wavenumber range. Careful consideration of the merits and of the limitations of these different spectral techniques for different source distribution models may lead to robust and geologically meaningful outcomes. In fact, despite the several different approaches all the methods give quite consistent and often similar estimates of the source depths. However, due to ambiguities on the correction spectral factor, the best estimates are obtained if this factor is constrained by a priori information. Finally, we estimate the depth to the magnetic sources beneath Sicily, which may provide additional constraints to better understand the deep crustal geometry and thermal gradients of the region.</p>

A review on spectral analysis of magnetic data for depth estimation

Geophysics ◽  
2021 ◽  
pp. 1-87
Author(s):  
Y. Kelemework ◽  
M. Fedi ◽  
M. Milano
Keyword(s):  
Spectral Analysis ◽  
Gravity Data ◽  
Window Size ◽  
Depth Estimation ◽  
Critical Parameters ◽  
Estimation Methods ◽  
Magnetic Data ◽  
Moho Depth ◽  
Exponential Factor ◽  
Temperature Isotherm

Spectral analysis has been used for studying a variety of geological structures and processes, such as estimation of the depth to the crystalline basement or of the Curie temperature isotherm from magnetic anomalies. However, the analysis is not standard, as it refers to different theoretical frameworks, such as statistical ensembles of homogeneous sources and uncorrelated or fractal random distributed sources. In this review, we aim to unify the approaches by reformulating all the common spectral expressions in the form of a product between a depth-dependent exponential factor and a factor, which we call the spectral correction factor, that incorporates all of the a priori assumptions for each method. This kind of organization might be useful for practitioners to quickly select the most appropriate method for a given study area. We also establish a new formula for extending the Spector and Grant method to the centroid depth estimation. Practical constraints on the depth estimation and intrinsic assumptions/limitations of the different approaches are examined by generating synthetic data of homogenous ensemble sources, random and fractal models. We address the statistical uncertainty of depth estimates using ordinary error propagation on the spectral slope. Critical parameters, such as the window size, are also analyzed in terms of the type of method used and of the geological complexity. We find that the window size is smaller for the centroid/modified centroid methods and larger for the spectral peak, de-fractal, and nonlinear parameter depth estimation methods. In any case, the window size can be large in tectonically stable regions and relatively small over volcanically, tectonically, and geothermally active areas. We finally estimate and discuss the depth to magnetic top and bottom in the Adriatic Sea region (eastern Italy) in the context of heat flow, Moho depth, and gravity data of the region.

scholarly journals Understanding Financial Instability: Minsky Versus the Austrians

2016 ◽  
Vol 22 (1) ◽  
Author(s):  
Ludwig Van Den Hauwe
Keyword(s):  
Financial Crisis ◽  
Global Financial Crisis ◽  
Critical Evaluation ◽  
Central Planning ◽  
Financial Instability ◽  
Conceptual Level ◽  
Theoretical Frameworks ◽  
Historical Experience ◽  
The Global Financial Crisis ◽  
Cross Fertilization

AbstractAlthough Minsky’s interpretation of Keynes’s macroeconomics and essential message clashes with authoritative alternative interpretations, it has become increasingly influential during the years following the Global Financial Crisis, even in mainstream circles. This paper offers a critical evaluation of Minsky’s Financial Instability Hypothesis from the perspective of the alternative Austro-Wicksellian paradigm. Although some of the similarities and/or analogies between Minsky’s approach and that of the Austrian School suggest a more than merely superficial affinity between the two theoretical frameworks and although some scope for cross-fertilization between both approaches can be found, both theoretically and empirically, at a fundamental conceptual level both theories remain incompatible and difficult if not impossible to reconcile, in particular in terms of fundamental causality and in terms of policy conclusions and prescriptions. Despite the fact that Minsky’s policy conclusions are multifaceted and somewhat eclectic, they manifest a lack of familiarity with the conclusions of the Austrian analysis of the problems of central planning by Big Players such as Big Bank and Big Government. Both approaches also offer contrasting interpretations of the historical experience of the Global Financial Crisis.

scholarly journals Optical Coherence Tomography as a Tool for Ocular Dynamics Estimation

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Damian Siedlecki ◽  
Waldemar Kowalik ◽  
Henryk Kasprzak
Keyword(s):  
Heart Rate ◽  
Optical Coherence Tomography ◽  
Spectral Analysis ◽  
High Speed ◽  
Anterior Segment ◽  
Power Spectra ◽  
Optical Coherence ◽  
Tomographic Images ◽  
Noninvasive Estimation ◽  
Ocular Hemodynamics

Purpose. The aim of the study is to demonstrate that the ocular dynamics of the anterior chamber of the eye can be estimated quantitatively by means of optical coherence tomography (OCT).Methods. A commercial high speed, high resolution optical coherence tomographer was used. The sequences of tomographic images of the iridocorneal angle of three subjects were captured and each image from the sequence was processed in MATLAB environment in order to detect and identify the contours of the cornea and iris. The data on pulsatile displacements of the cornea and iris and the changes of the depth of the gap between them were retrieved from the sequences. Finally, the spectral analysis of the changes of these parameters was performed.Results. The results of the temporal and spectral analysis manifest the ocular microfluctuation that might be associated with breathing (manifested by 0.25 Hz peak in the power spectra), heart rate (1–1.5 Hz peak), and ocular hemodynamics (3.75–4.5 Hz peak).Conclusions. This paper shows that the optical coherence tomography can be used as a tool for noninvasive estimation of the ocular dynamics of the anterior segment of the eye, but its usability in diagnostics of the ocular hemodynamics needs further investigations.

Spectral analysis of the EMG and diaphragmatic muscle fatigue during periodic breathing in infants

1985 ◽  
Vol 58 (3) ◽  
pp. 830-833 ◽  
Author(s):  
S. T. Nugent ◽  
J. P. Finley
Keyword(s):  
Spectral Analysis ◽  
Muscle Fatigue ◽  
Preterm Infants ◽  
High Frequency ◽  
Power Spectra ◽  
Low Frequency ◽  
Periodic Breathing ◽  
Full Term ◽  
Diaphragmatic Muscle ◽  
Normal Breathing

Periodic breathing occurs commonly in full-term and preterm infants. The mechanisms which switch breathing on and off within a cycle of periodic breathing are not certain. Since immature infants may experience diaphragmatic muscle fatigue, one potential switching mechanism is fatigue. Power spectra of the electromyogram, uncontaminated by the electrocardiograph artifact, were studied for evidence of diaphragmatic muscle fatigue during spontaneous periodic breathing in infants. A fall in the high-frequency (103–600 Hz) power and an increase in the low-frequency (23–47 Hz) power during periodic as compared with normal breathing would indicate fatigue. This effect was not observed in any of the infants studied. Hence, there is no evidence that periodic breathing is the result of diaphragmatic muscle fatigue. This finding suggests that the effect of drugs such as theophylline in eliminating periodic breathing may be unrelated to the fact that they also reduce fatigue.

Complex and power spectra of optical signals using time-dispersion spectral analysis

2012 ◽  
Author(s):  
Arseny Zhdanov ◽  
Vasily Kazakov ◽  
Oleg Moskaletz
Keyword(s):  
Spectral Analysis ◽  
Power Spectra ◽  
Optical Signals ◽  
Time Dispersion

scholarly journals Estimating the volume of glaciers in the Himalayan–Karakoram region using different methods

2014 ◽  
Vol 8 (6) ◽  
pp. 2313-2333 ◽  
Author(s):  
H. Frey ◽  
H. Machguth ◽  
M. Huss ◽  
C. Huggel ◽  
S. Bajracharya ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
Critical Evaluation ◽  
Estimation Method ◽  
Volume Estimation ◽  
Ice Thickness ◽  
Model Parameters ◽  
Distribution Models ◽  
Ice Volume ◽  
Sensitivity Assessment ◽  
Volume Estimates

Abstract. Ice volume estimates are crucial for assessing water reserves stored in glaciers. Due to its large glacier coverage, such estimates are of particular interest for the Himalayan–Karakoram (HK) region. In this study, different existing methodologies are used to estimate the ice reserves: three area–volume relations, one slope-dependent volume estimation method, and two ice-thickness distribution models are applied to a recent, detailed, and complete glacier inventory of the HK region, spanning over the period 2000–2010 and revealing an ice coverage of 40 775 km2. An uncertainty and sensitivity assessment is performed to investigate the influence of the observed glacier area and important model parameters on the resulting total ice volume. Results of the two ice-thickness distribution models are validated with local ice-thickness measurements at six glaciers. The resulting ice volumes for the entire HK region range from 2955 to 4737 km3, depending on the approach. This range is lower than most previous estimates. Results from the ice thickness distribution models and the slope-dependent thickness estimations agree well with measured local ice thicknesses. However, total volume estimates from area-related relations are larger than those from other approaches. The study provides evidence on the significant effect of the selected method on results and underlines the importance of a careful and critical evaluation.

Spectral analysis of hemodynamics during infusions of epinephrine and norepinephrine in men

1994 ◽  
Vol 76 (5) ◽  
pp. 1914-1921 ◽  
Author(s):  
J. H. Tulen ◽  
A. J. Man in ′t Veld ◽  
A. M. Van Roon ◽  
P. Moleman ◽  
H. G. Van Steenis ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Plasma Concentrations ◽  
Power Spectra ◽  
Low Frequency ◽  
Cardiovascular Control ◽  
Control Mechanisms ◽  
Short Term ◽  
Arterial Blood ◽  
Frequency Fluctuations ◽  
Infusion Of Norepinephrine

Spectral analysis of fluctuations in heart rate (HR) and arterial blood pressure (BP) during a 6-h infusion of epinephrine (15 ng.kg-1.min-1) or norepinephrine (30 ng.kg-1.min-1) in 10 normotensive males was used to analyze effects of peripheral sympathetic nervous system activity and adrenal medullary discharge on cardiovascular variability. Power spectra were calculated for each 5-min period for HR, systolic BP, and diastolic BP to yield power values for three frequency bands: low (0.02–0.06 Hz), mid (0.07–0.14 Hz), and high (0.15–0.40 Hz). Infusion of epinephrine and norepinephrine induced plasma concentrations of epinephrine and norepinephrine, respectively, within the high physiological range. Spectral analysis showed that low-frequency fluctuations of BP during infusions of epinephrine and midfrequency fluctuations of BP during infusion of norepinephrine changed in opposite directions. These fluctuations may represent different components of short-term cardiovascular control mechanisms during situations that mimic increased sympathoadrenal activity. No changes were observed in HR fluctuations or high-frequency fluctuations of BP after either catecholamine. Our data imply that changes in concentrations of circulating catecholamines cannot be unequivocally labeled as indexes of an altered sympathoadrenal involvement in short-term cardiovascular control.

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