Characterization of geological boundaries using 1‐D wavelet transform on gravity data: Theory and application to the Himalayas

International audienceWe investigate the use of the continuous wavelet transform for gravity inversion. The wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source-analysis tool. Here we develop an inverse scheme in the wavelet domain , designed to recover the geometric characteristics of density heterogeneities described by simple-shaped sources. The 1-D analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order. In the gravity case, we first demonstrate how to localize causative sources using simple geometric constructions. Both the upper part of the source and the whole source can be studied when considering low or high altitudes, respectively. The ho-mogeneity degree of the source is deduced without prior information and allows us to infer its shape. Introducing complex wavelets, we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources. The modulus term is used in an inversion procedure to recover the thickness of the source. The phase term provides its dip. This analysis is performed on gravity data we measured along a profile across the Himalayas in Nepal. Good agreement of our results with well-documented thrusting structures demonstrates the applicability of the method to real data. Also, deeper, less constrained structures are characterized

Late Hercynian leucogranites modelling as deduced from new gravity data: The example of the Millevaches massif (Massif Central, France)

The Millevaches granitic complex, located in the northern part of the French Massif Central, is elongated in a N-S direction, perpendicular to the main E-W trend of the Hercynian belt. It is affected on its limits and in its core by several ductile shear zones that have necessarily played a great role in the emplacement and exhumation of the massif. Based on gravity modelling and recent field observations, this study intends to highlight the massif structure at depth and discuss its mode of emplacement and relations with the surrounding terrains. The new gravity and density measurements on the north-east part of the Millevaches massif improve the gravity coverage of the northern Limousin. Using these new data we model the deep structure of the Millevaches plateau. The density measurements made on the different types of granites of the massif, and on the surrounding terrains improve the interpretation of the Bouguer anomaly. Analysis and inversion of the residual Bouguer anomaly in the area show that the Millevaches massif is 2 to 4 km-thick, from north to south and from west to east, locally rooting down to about 6 km deep in its eastern and southern terminations. These two zones coincide with porphyritic plutons and, because of the complex composite structure of the massif, cannot be definitively interpreted as feeding zones. In the field, the N-S-oriented Pradines vertical fault affects the core of the massif on 4 to 5 km width. Microstructural observations evidence that the faulting is contemporaneous of the granites emplacement. We suggest that this tectonic lineament could have triggered the migration of the magma, although it is not related to a clear gravity anomaly. AMS measurements in the north-central part of the Millevaches massif suggest that the magnetic foliation and lineation display a general sub-horizontal pattern. Moreover, on the western border of the Millevaches massif, the Argentat deep seismic profile shows sub-horizontal layering of gneisses and micaschists and evidences normal faulting offset of this layering along Argentat fault. This agrees fairly well with the gravity results, suggesting that (i) the Millevaches massif would be at a high structural level in the crust, (ii) the exhumation of the massif would have been favoured along the Argentat normal fault. As a whole, the massif can be described as a laccolith, 2 to 4 km-thick, emplaced as a "magmatic lens" into the sub-horizontally foliated gneisses and micaschists

Gravity anomalies, crustal structure and thermo-mechanical support of the Himalaya of Central Nepal

We use two gravity profiles that we measured across Central Nepal, in conjunction with existing data, to constrain the mechanical behaviour and the petrological structure of the lithosphere in the Himalayan collision zone. The data show (1) overcompensation of the foreland and undercompensation of the Higher Himalaya, as expected from the flexural support of the range; (2) a steep gravity gradient of the order of 1.3 mgal km^(−1) beneath the Higher Himalaya, suggesting a locally steeper Moho; and (3) a 10 km wide hinge in southern Tibet. We compare these data with a 2-D mechanical model in which the Indian lithosphere is flexed down by the advancing front of the range and sedimentation in the foreland. The model assumes brittle Coulomb failure and non-linear ductile flow that depends on local temperature, which is computed from a steady-state thermal model. The computed Moho fits seismological constraints and is consistent with the main trends in the observed Bouguer anomaly. It predicts an equivalent elastic thickness of 40–50 km in the foreland. The flexural rigidity decreases northwards due to thermal and flexural weakening, resulting in a steeper Moho dip beneath the high range. Residuals at short wavelengths (over distances of 20–30 km) are interpreted in terms of (1) sediment compaction in the foreland (Δρ = 150 kg m^(−3) between the Lower and Middle Siwaliks); (2) the contact between the Tertiary molasse and the meta-sediments of the Lesser Himalaya at the MBT (Δρ = 220 kg m^(−3)); and (3) the Palung granite intrusion in the Lesser Himalaya (Δρ = 80 kg m^(−3)). Finally, if petrological transformations expected from the local (P, T) are assumed, a gravity signature of the order of 250 mgal is predicted north of the Lesser Himalaya, essentially due to eclogitization of the lower crust, which is inconsistent with the gravity data. We conclude that eclogitization of the Indian crust does not take place as expected from a steady-state local equilibrium assumption. We show, however, that eclogitization might actually occur beneath southern Tibet, where it could explain the hinge observed in the gravity data. We suspect that these eclogites are subducted with the Indian lithosphere

Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).

Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)

Improved risk stratification of patients with atrial fibrillation: an integrated GARFIELD-AF tool for the prediction of mortality, stroke and bleed in patients with and without anticoagulation.

OBJECTIVES: To provide an accurate, web-based tool for stratifying patients with atrial fibrillation to facilitate decisions on the potential benefits/risks of anticoagulation, based on mortality, stroke and bleeding risks. DESIGN: The new tool was developed, using stepwise regression, for all and then applied to lower risk patients. C-statistics were compared with CHA2DS2-VASc using 30-fold cross-validation to control for overfitting. External validation was undertaken in an independent dataset, Outcome Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF). PARTICIPANTS: Data from 39 898 patients enrolled in the prospective GARFIELD-AF registry provided the basis for deriving and validating an integrated risk tool to predict stroke risk, mortality and bleeding risk. RESULTS: The discriminatory value of the GARFIELD-AF risk model was superior to CHA2DS2-VASc for patients with or without anticoagulation. C-statistics (95% CI) for all-cause mortality, ischaemic stroke/systemic embolism and haemorrhagic stroke/major bleeding (treated patients) were: 0.77 (0.76 to 0.78), 0.69 (0.67 to 0.71) and 0.66 (0.62 to 0.69), respectively, for the GARFIELD-AF risk models, and 0.66 (0.64-0.67), 0.64 (0.61-0.66) and 0.64 (0.61-0.68), respectively, for CHA2DS2-VASc (or HAS-BLED for bleeding). In very low to low risk patients (CHA2DS2-VASc 0 or 1 (men) and 1 or 2 (women)), the CHA2DS2-VASc and HAS-BLED (for bleeding) scores offered weak discriminatory value for mortality, stroke/systemic embolism and major bleeding. C-statistics for the GARFIELD-AF risk tool were 0.69 (0.64 to 0.75), 0.65 (0.56 to 0.73) and 0.60 (0.47 to 0.73) for each end point, respectively, versus 0.50 (0.45 to 0.55), 0.59 (0.50 to 0.67) and 0.55 (0.53 to 0.56) for CHA2DS2-VASc (or HAS-BLED for bleeding). Upon validation in the ORBIT-AF population, C-statistics showed that the GARFIELD-AF risk tool was effective for predicting 1-year all-cause mortality using the full and simplified model for all-cause mortality: C-statistics 0.75 (0.73 to 0.77) and 0.75 (0.73 to 0.77), respectively, and for predicting for any stroke or systemic embolism over 1 year, C-statistics 0.68 (0.62 to 0.74). CONCLUSIONS: Performance of the GARFIELD-AF risk tool was superior to CHA2DS2-VASc in predicting stroke and mortality and superior to HAS-BLED for bleeding, overall and in lower risk patients. The GARFIELD-AF tool has the potential for incorporation in routine electronic systems, and for the first time, permits simultaneous evaluation of ischaemic stroke, mortality and bleeding risks. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier for GARFIELD-AF (NCT01090362) and for ORBIT-AF (NCT01165710)

Two-year outcomes of patients with newly diagnosed atrial fibrillation: results from GARFIELD-AF.

AIMS: The relationship between outcomes and time after diagnosis for patients with non-valvular atrial fibrillation (NVAF) is poorly defined, especially beyond the first year. METHODS AND RESULTS: GARFIELD-AF is an ongoing, global observational study of adults with newly diagnosed NVAF. Two-year outcomes of 17 162 patients prospectively enrolled in GARFIELD-AF were analysed in light of baseline characteristics, risk profiles for stroke/systemic embolism (SE), and antithrombotic therapy. The mean (standard deviation) age was 69.8 (11.4) years, 43.8% were women, and the mean CHA2DS2-VASc score was 3.3 (1.6); 60.8% of patients were prescribed anticoagulant therapy with/without antiplatelet (AP) therapy, 27.4% AP monotherapy, and 11.8% no antithrombotic therapy. At 2-year follow-up, all-cause mortality, stroke/SE, and major bleeding had occurred at a rate (95% confidence interval) of 3.83 (3.62; 4.05), 1.25 (1.13; 1.38), and 0.70 (0.62; 0.81) per 100 person-years, respectively. Rates for all three major events were highest during the first 4 months. Congestive heart failure, acute coronary syndromes, sudden/unwitnessed death, malignancy, respiratory failure, and infection/sepsis accounted for 65% of all known causes of death and strokes for <10%. Anticoagulant treatment was associated with a 35% lower risk of death. CONCLUSION: The most frequent of the three major outcome measures was death, whose most common causes are not known to be significantly influenced by anticoagulation. This suggests that a more comprehensive approach to the management of NVAF may be needed to improve outcome. This could include, in addition to anticoagulation, interventions targeting modifiable, cause-specific risk factors for death. CLINICAL TRIAL REGISTRATION: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

Implications of serial measurements of natriuretic peptides in heart failure: insights from BIOSTAT‐CHF

No abstract available

Gravity inversion, AMS and geochronological investigations of syntectonic granitic plutons in the southern part of the Variscan French Massif Central

Magnetic fabric analyses, gravity inversion associated with chemical U-Th-Pb dating and structural observations are carried out to elucidate relationships between faulting and magmatic processes. This multidisciplinary study has been undertaken on Late Carboniferous plutons, situated in the southern part of the Variscan French Massif Central (FMC). The Glénat, Omps and Boisset plutons crop out on both sides of the crustal-scale Sillon Houiller Fault (SHF). The Anisotropy of Magnetic Susceptibility (AMS) measurements and structural observations show that (i) the plutons acquired their final structure during the magma crystallization and record a NW-SE maximum stretching trend; (ii) in the Boisset pluton, post-magmatic fabrics predominate with a NNW-SSE trending lineation. The structural pattern deduced from the AMS study is thus consistent with the NW-SE late orogenic extensional tectonic regime that has been documented in other parts of the FMC during Late Carboniferous. The 3D geological modelling refined by 3D gravity inversion does not show any evidence of rooting of the granites along the SHF. Therefore, despite the apparent cartographic relationship between the SHF and the three plutons, our study does not support a genetic link between fault and plutons. It also questions the existence of the SHF in this part of the Massif Central at the time of pluton emplacement, and emphasises the dominant role of the regional tectonic framework rather than local faulting as a factor controlling pluton emplacement. © 2009 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex

Traité de géométrie descriptive suivi de la méthode des plans cotés et de la théorie des engrenages cylindriques et coniques, avec une collection d¬épures, composée de 71 planches

Contiene: Tome premier: Texte. - XX, 369. Tome second: Planches. - 71 h. de gra

3-D modelling of Alpine Mohos in Southwestern Alps

International audienceWe present and discuss a 3-D geometrical model of the Moho topography in the Southwestern Alps. To achieve this objective, we used the potential of 3-D modelling software (i.e. a 3-D GeoModeller) to combine gravity, seismic and seismological constraints in a same and coherent 3-D space. A new regional Bouguer gravity anomaly map of the Southwestern Alps was calculated and filtered to isolate the Moho signature in the Southwestern Alps. Then, two alternative 3-D models were computed with data from the literature based on seismic and seismological constraints. The first one represents an European lithospheric mantle decoupled from the European orogenic crust which is back-thrusted by the Ivrea body whereas the second 3-D model illustrates the subduction of a 20-km-thick piece of lower continental crust, coupled with the European upper mantle, beneath the Ivrea body. According to the geological knowledge of these units we then assigned a density value to each modelled layer and we computed their gravity effects to compare them with the filtered Moho map of the Southwestern Alps. First of all, the significant discrepancies of the Moho gravity signature generated by these two geometrical models reveal that subduction of continental crust is no more active in the present-day configuration of the Southwestern Alps. Therefore, the first 3-D model was refined by a stochastic 3-D gravity inversion. Based on this processing, our investigations confirm the presence of three superposed Mohos in the Southwestern Alps and underline that: (i) The crust/mantle European boundary is localized around 50 km depth beneath the Argentera-Mercantour massif, (ii) The European lithospheric mantle is decoupled from the European orogenic crust, (iii) The Adriatic mantle (Ivrea body) is split into two distinct units; the upper unit is located at 10 km depth beneath the Dora-Maïra massif, and the lower unit extends from 20 to 45 km depth. (iv) These two mantle indenters affect differently the European crust and are responsible for the localization of crustal deformation and for strain partitioning in the Southwestern Alps