Estimation of poroelastic parameters from seismograms using Biot theory

We investigate the possibility to extract information contained in seismic waveforms propagating in fluid-filled porous media by developing and using a full waveform inversion procedure valid for layered structures. To reach this objective, we first solve the forward problem by implementing the Biot theory in a reflectivity-type simulation program. We then study the sensitivity of the seismic response of stratified media to the poroelastic parameters. Our numerical tests indicate that the porosity and consolidation parameter are the most sensitive parameters in forward and inverse modeling, whereas the permeability has only a very limited influence on the seismic response. Next, the analytical expressions of the sensitivity operators are introduced in a generalized least-square inversion algorithm based on an iterative modeling of the seismic waveforms. The application of this inversion procedure to synthetic data shows that the porosity as well as the fluid and solid parameters can be correctly reconstructed as long as the other parameters are well known. However, the strong seismic coupling between some of the model parameters makes it difficult to fully characterize the medium by a multi-parameter inversion scheme. One solution to circumvent this difficulty is to combine several model parameters according to rock physics laws to invert for composite parameters. Another possibility is to invert the seismic data for the perturbations of the medium properties, such as those resulting from a gas injection

Full waveform inversion of shot gathers in terms of poro-elastic parameters

International audienceWe have developed a full waveform iterative inversion procedure for determining the porosity, permeability, interstitial fluid properties and mechanical parameters of stratified porous media. The inverse problem is solved by using a generalized least-squares formalism. The proposed method achieves computational efficiency through semi-analytical, semi-numerical solutions for calculating the reference and perturbation wave fields from Biot's theory. When this algorithm is applied to noise-free synthetic data, it is found that the inversion of a single parameter as a function of depth generally yields satisfactory results. However, simultaneous or sequential multi-parameter inversions underline, as expected, the inter-dependence between parameters having different physical dimensionality. The strong correlations that may exist between parameters of different types remain a major issue in multiparameter estimation, but viable solutions may be found when some a priori knowledge of the porous medium is available. For instance, the seismic data can be inverted for the saturation rate by knowing the properties of the interstitial fluid. Nevertheless, the approach proposed here militates in favor of a combination of different methods to solve the challenging task of estimating poro-elastic parameters from seismic data

Using a Poroelastic Theory to Reconstruct Subsurface Properties: Numerical Investigation

International audienceThe quantitative imaging of the Earth subsurface is a major challenge in geophysics. In oil and gas exploration and production, aquifer management and other applications such as the underground storage of CO2 , seismic imaging techniques are implemented to provide as much information as possible on fluid-filled reservoir rocks. Biot theory (Biot, 1956) and its extensions provide a convenient framework to connect the various parameters characterizing a porous medium to the wave properties, namely, their amplitudes, velocities and frequency contents. The poroelastic model involves more parameters than the elastodynamic theory, but on the other hand, the wave attenuation and dispersion characteristics at the macroscopic scale are determined by the intrinsic properties of the medium without having to resort to empirical relationships

Applicability of the University of Pennsylvania Smell Identification Test (SIT) in Brazilians: pilot study

O teste de identificação do olfato da Universidade da Pensilvânia (SIT) é o exame olfatório mais citado na literatura devido a sua fácil aplicação e alta confiabilidade teste-reteste. Ainda não foram normatizados seus valores de olfação normal para a população brasileira. OBJETIVO: Verificar o escore no SIT alcançado por um grupo de brasileiros e o nível de dificuldade encontrado para a execução do teste. FORMA DE ESTUDO: Transversal. MATERIAL E MÉTODO: O SIT foi aplicado a 25 voluntários brasileiros de diversas classes econômicas, sem queixas olfatórias prévias. Após a aplicação do teste, todos preencheram um questionário com uma escala visual analógica (VAS) referente ao nível de dificuldade encontrado na realização do teste. RESULTADOS: O escore médio da amostra de brasileiros foi 32,5 (desvio-padrão:3,48) de 40, abaixo do considerado normal para a população americana. O nível de dificuldade médio encontrado foi 26mm (desvio padrão: 24,68) segundo a VAS, tendendo a facilidade, e 4(16%) participantes não conheciam algum dos odores escritos nas alternativas. CONCLUSÃO: Nesse estudo piloto, houve indícios de boa aplicabilidade do teste, com o escore dos brasileiros pouco abaixo da normosmia. São necessários estudos futuros para confirmar a existência de diferença de pontuação entre pessoas de diferente classe econômica.The University of Pennsylvania Smell Identification Test (SIT) is the most cited olfactory test in the literature because it is easy to perform and there is high test-retest reliability. There were no standardized olfaction values in a normal Brazilian population. AIM: To measure the SIT score in a group of Brazilians, and to assess the level of difficulty when implementing the test. STUDY DESIGN: A cross-sectional study. MATERIALS AND METHODS: The SIT was applied in 25 Brazilian volunteers of various income levels who presented no olfactory complaints. Following the test, subjects answered a questionnaire with a visual analog scale (VAS) for the level of difficulty. RESULTS: The mean in the sample of Brazilians was 32.5 (SD: 3.48) our of 40; this is below what is considered normal for US citizens. The level of difficulty was on average 26 mm (SD: 24.68) in the VAS, but it trended towards easy; 4(16%) participants did not recognize some of the odors under 'alternatives'. CONCLUSION: In this pilot study, there was evidence of good test applicability; the score of the sample of Brazilians was just below normosmia. Further studies are needed to confirm the existence of differences between people of different income levels

Source geometry from exceptionally high resolution long period event observations at Mt Etna during the 2008 eruption

During the second half of June, 2008, 50 broadband seismic stations were deployed on Mt Etna volcano in close proximity to the summit, allowing us to observe seismic activity with exceptionally high resolution. 129 long period events (LP) with dominant frequencies ranging between 0.3 and 1.2 Hz, were extracted from this dataset. These events form two families of similar waveforms with different temporal distributions. Event locations are performed by cross-correlating signals for all pairs of stations in a two-step scheme. In the first step, the absolute location of the centre of the clusters was found. In the second step, all events are located using this position. The hypocentres are found at shallow depths (20 to 700 m deep) below the summit craters. The very high location resolution allows us to detect the temporal migration of the events along a dike-like structure and 2 pipe shaped bodies, yielding an unprecedented view of some elements of the shallow plumbing system at Mount Etna. These events do not seem to be a direct indicator of the ongoing lava flow or magma upwelling

Crustal structure below Popocat\'epetl Volcano (Mexico) from analysis of Rayleigh waves

An array of ten broadband stations was installed on the Popocat\'epetl volcano (Mexico) for five months between October 2002 and February 2003. 26 regional and teleseismic earthquakes were selected and filtered in the frequency time domain to extract the fundamental mode of the Rayleigh wave. The average dispersion curve was obtained in two steps. Firstly, phase velocities were measured in the period range [2-50] s from the phase difference between pairs of stations, using Wiener filtering. Secondly, the average dispersion curve was calculated by combining observations from all events in order to reduce diffraction effects. The inversion of the mean phase velocity yielded a crustal model for the volcano which is consistent with previous models of the Mexican Volcanic Belt. The overall crustal structure beneath Popocat\'epetl is therefore not different from the surrounding area, and the velocities in the lower crust are confirmed to be relatively low. Lateral variations of the structure were also investigated by dividing the network into four parts and by applying the same procedure to each sub-array. No well-defined anomalies appeared for the two sub-arrays for which it was possible to measure a dispersion curve. However, dispersion curves associated with individual events reveal important diffraction for 6 s to 12 s periods which could correspond to strong lateral variations at 5 to 10 km depth

Diagnóstico de anemia por deficiência de ferro em crianças do Nordeste do Brasil

OBJECTIVE: To diagnose iron deficiency anemia in children. METHODS: The study was conducted with a sample of 301 children aged six to 30 months attending public daycare centers in the city of Recife, Northeast Brazil, in 2004. The diagnoses of anemia were based on a combination of different hematological and biochemical parameters: hemoglobin, mean corpuscular volume, ferritin, C-reactive protein, transferrin saturation and transferrin receptor. The chi-square test and ANOVA were used in the statistical analysis. RESULTS: Of all children studied, 92.4% had anemia (HbOBJETIVO: Diagnosticar anemia por deficiencia de hierro en niños. MÉTODOS: El estudio fue desarrollado con una muestra de 301 niños con edades entre seis y 30 meses, usuarios de guarderías públicas de Recife, Noreste de Brasil, en 2004. Para el diagnóstico de la anemia se utilizó la combinación de diferentes parámetros hematológicos y bioquímicos: hemoglobina, volumen corpuscular promedio, ferritina, proteína C-reactiva, saturación de la transferrina y receptor de la transferrina. Para el análisis estadístico se empleó la prueba de chi-cuadrado y ANOVA. RESULTADOS: Del total de niños, 92,4% tenían anemia (HbOBJETIVO: Diagnosticar anemia por deficiência de ferro em crianças. MÉTODOS: O estudo foi desenvolvido com uma amostra de 301 crianças com idade entre seis e 30 meses, usuárias de creches públicas de Recife, PE, em 2004. Para o diagnóstico da anemia utilizou-se a combinação de diferentes parâmetros hematológicos e bioquímicos: hemoglobina, volume corpuscular médio, ferritina, proteína C-reativa, saturação da transferrina e receptor da transferrina. Para a análise estatística empregou-se o teste do qui-quadrado e ANOVA. RESULTADOS: Do total de crianças, 92,4% tinha anemia (Hb < 110g/L) e 28,9% apresentou anemia moderada/grave (H

Giant cell bone lesions in the craniofacial region: a diagnostic and therapeutic challenge

Background: Giant cell tumors of bone (GCTs) are common in the long bones, but rare in the craniofacial region, with only 1% of cases occurring in the latter. Clinical, radiological, and anatomical diagnosis of this locally aggressive disease, which occurs in response to trauma or neoplastic transformation, poses a major challenge in clinical practice. Methods: The present study describes a series of 4 cases and highlights the main features of the differential diagnosis and treatment of these lesions: GCT, giant cell reparative granuloma (GCRG), and the brown tumor of hyperparathyroidism. Results: GCT presents as a benign neoplasm, most typically affecting the knees, and rarely in the temporal and sphenoid bones. It is radiologically indistinguishable from GCRG due to its lytic, poorly defined appearance. The distinction can only be made microscopically, as the presence of multinucleated giant cells scattered throughout the stroma and the absence of a history of trauma favor a diagnosis of GCT. The brown tumor of hyperparathyroidism occurs with rapid, localized osteoclast activity secondary to the effects of increased parathyroid hormone (PTH) levels; parathyroid examination is indispensable. Conclusion: The diagnosis and treatment of these lesions poses a major challenge due to their similar clinical presentation and radiological appearance. Accurate diagnosis is essential for definition of appropriate management, as complete resection is the goal in GCT and GCRG to avoid recurrence, whereas the brown tumor often yields to treatment of the underlying hyperparathyroidism

Daily, biweekly, and seasonal temporal scales of pCO2 variability in two stratified Mediterranean reservoirs

Temporal scales of variability for the partial pressure of CO2 (pCO2) in the surface waters of two stratified Mediterranean reservoirs were examined through the temporal decomposition of 5 month time series with hourly sampling frequency. pCO2 time series included similar patterns of variability at daily,biweekly, and seasonal scales regardless of the difference in amplitude of the pCO2 variation in the two reservoirs studied. Daily variability was strongly related to the day-night cycles of metabolic activity, accounting for about one third of the total amplitude in pCO2 variation. At a biweekly scale, wind forcing led to higher rates of air-water CO2 exchange and subsequently temporary partial mixing events associated to relevant increase of CO2 concentration in surface waters. Seasonal variability accounted for one third of the amplitude of the pCO2 variability and was coupled to the seasonal dynamics of water temperature and thermal stratification of the water column. Our results provide evidence that CO2 emission from stratified water bodies shows significant variability at daily, biweekly, and seasonal scales; all of which should be taken into consideration in the analyses of the carbon fluxes. The wind-induced mixing events, operating at temporal scales between daily and seasonal cycles, may become a major factor controlling the pCO2 dynamics. Hence, some of the most common models for computing CO2 fluxes from pCO2 were not able to reproduce the biweekly response patterns of CO2 emissions to wind forcing