33 research outputs found
Analysis of far-field erosion induced by low-crested rubble-mound structures
No full textThis paper focuses on the analysis of the morphological response induced by low-crested structures on the adjacent seabed, with emphasis on the far-field erosion that is frequently observed close to roundheads and at the gaps between structures. The analysis is based on observations of far-field erosion, both at prototype scale and in laboratory experiments. Mechanisms responsible for the observed erosion are highlighted using coastal area numerical modelling tools to simulate the flow patterns induced by schemes involving low-crested structures. Finally, an example of the use of a coastal area morphological modelling system to investigate the dependence of the far-field erosion processes on the freeboard of the coastal protection structures is presented and discussed
Ruido 1/f y reversiones del momento dipolar magnético para diferentes dínamos esféricos
No full textHace más de un siglo que Bernard Brunhes propuso la existencia de reversiones del campo magnético terrestre en escalas de tiempo geológicas. Esta teoría, hacia mediados del siglo XX, logró la aceptación de la comunidad científica. No obstante, aún no ha sido posible establecer mecanismos precisos que permitan explicar las reversiones geomagnéticas. El presente trabajo muestra que, aún en una geometría sencilla, las ecuaciones de la magnetohidrodinámica difusiva y rotante contienen todos los ingredientes para reproducir satisfactoriamente numerosos rasgos del campo magnético terrestre, entre ellos los cambios en la polaridad del momento dipolar magnético. Asimismo se verifica la existencia de un extenso rango de frecuencias donde el momento dipolar magnético presenta invariancia de escala, fenómeno conocido como ruido 1 / f . Se conjetura que esta última característica, asociada a la presencia de memoria de largo plazo en el sistema, posee relación directa con la aparición de reversiones.More than one century ago, Bernard Brunhes proposed the existence of reversals in Earth’s magnetic field at geological time scales. Halfway through the XX century, this theory got acceptance within the scientific community. Nonetheless, efforts to establish precise mechanisms to account for these reversals have been, so far, unsuccessful. In this work we show that, even for simple geometries, diffusive and rotating magnetohydrodynamic’s equations present the key ingredients to reproduce several features of the geomagnetic field, including polarity reversals of the magnetic dipole moment. Moreover we demonstrate the existence of a wide range of frequencies where dipole moment’s power spectrum presents scale invariance, a characteristic known as 1/f noise. We argue that this feature, associated to long-term memory phenomena, has a direct connection with the spontaneous flipping of the geomagnetic field.GeofísicoUniversidad Nacional de La PlataFacultad de Ciencias Astronómicas y Geofísica
Seismoelectric studies of coupled acoustic, elastic and poroelastic media
No full textEn el marco del plan de Doctorado en Geofísica se desarrollaron tres trabajos. El primero de ellos se titula "F. Bucher, F. Zyserman, L. Monachesi, G. Castromán. Modelado Numérico de Propagación de Ondas Sísmicas en Medios Poroelásticos Acoplados con Acústicos. Mecánica Computacional, Acoustics and Vibrations. Vol. 39-6, pp 137-146, 2022". En este estudio, se implementó un código de elementos finitos para simular la propagación de ondas sísmicas en un medio poroelástico acoplado con uno acústico, en un espacio unidimensional. Una característica a destacar de esta herramienta numérica es la posibilidad que brinda para diseñar modelos en donde medios acústicos y poroelásticos puedan tener geometrías heterogéneas.En el segundo artículo, publicado bajo el título "F. Bucher, L. Monachesi, G. Castromán, F. Zyserman. Seismoelectric response of 2D elastic/poroelastic media: A phenomenological approach. Geophysical Journal International. Vol. 236-1, pp 62-77, 2024", se presenta un modelo fenomenológico para describir la respuesta sismoeléctrica de una interfase que separa un medio elástico de otro poroso saturado. En resumen, se demuestra que las conversiones sismoeléctricas generadas por el arribo de una onda sísmica a la interfase (como la Respuesta de Interfase y las Ondas Evanescentes) pueden modelarse como la superposición de los campos generados por dipolos eléctricos cuasiestáticos, orientados según el ángulo de incidencia en cada punto de la interfase y activados con la llegada de la onda sísmica a dicha interfase. Además, el modelo se muestra robusto y adaptable, respondiendo adecuadamente a variaciones en las propiedades físicas de los medios y en la geometría de la interfase.Finalmente, en el tercer trabajo, "F. Bucher, F. Zyserman, L. Monachesi. Seismic wave propagation in coupled fluid and porous media: a finite element approach. Geophysical Prospecting. 2024", se generaliza el primer estudio del primer trabajo a medios bidimensionales. Este nuevo código, también basado en el método de elementos finitos, permite diseñar modelos con configuraciones arbitrarias de medios acústicos y poroelásticos, lo cual facilita la simulación de la propagación de ondas en entornos marinos complejos, como un fondo oceánico con topografía no horizontal, representando el agua como medio acústico y el lecho marino como medio poroso. Este software, denominado ACPE2D, también ha sido extendido al ámbito sismoeléctrico, con vistas a futuros desarrollos.Carrera: Doctorado en Geofísica
Lugar de trabajo: Otro
Organismo: CONICET
Año de inicio de beca: 2021
Año de finalización de beca: 2027
Apellido, Nombre del Director/a/e: Zyserman, Fabio
Apellido, Nombre del Codirector/a/e: Monachesi, Leonardo
Lugar de desarrollo: Otro
Áreas de conocimiento: Cs. de la Tierra y Planetarias
Tipo de investigación: AplicadaFacultad de Ciencias Astronómicas y Geofísica
A review on electrokinetically induced seismo-electrics, electro-seismics, and seismo-magnetics for Earth sciences
No full textInternational audienceThe seismo-electromagnetic method (SEM) can be used for non-invasive subsurface exploration. It shows interesting results for detecting fluids such as water, oil, gas, CO_2 , or ice, and also help to better characterise the subsur-face in terms of porosity, permeability, and fractures. However , the challenge of this method is the low level of the induced signals. We first describe SEM's theoretical background , and the role of some key parameters. We then detail recent studies on SEM, through theoretical and numerical developments , and through field and laboratory observations, to show that this method can bring advantages compared to classical geophysical methods
Numerical modelling of passive electroseismic surveying
No full textThis work reports numerical modelling of electroseismic conversions when the electric field source originates in the atmosphere. Layered structures of conductivity anomalies yield rotated electric fields at reservoir depths as large as source fields at the surface. Active-source electroseismic field tests imaged reservoirs 1800 m deep. However, the required high-power, dipole sources mediate against these methods finding practical application in hydrocarbon exploration. We extend previous research by considering the potential for using environmental electric fields to create useful electroseismic conversions. World-wide lightning strikes induce time-dependent electric fields in the atmosphere. In the frequency band appropriate for seismic surveying, 1-100 Hz, electromagnetic field pulses occur at a rate of 10-100 pulses per second. These pulses create horizontal electric fields in the earth's surface that induce electric currents in the subsoil. Those currents preferentially channel through high-conductivity layers. Charge accumulates at the termini of conducting layers. That charge accumulation induces galvanic currents. Vertical galvanic currents propagate to depth where they generate propagating seismic waves at gradients in electrical properties, such as conductivity gradients at reservoirs. We use 2-D numerical simulations on three different, layered-earth models to estimate the seismic amplitudes generated by passive fields. The modelling shows that the transverse magnetic fields can induce potentially useful vertical electric fields at depth. The generated seismic amplitudes at the top of the reservoir are sensitive to the oil content of the reservoir, the frequency of the primary electric field, the geometry of the conducting layers and various material properties. Finally, a hypothetical laterally complex reservoir configuration was tested which confirms the mentioned results and additionally shows the ability of the proposed method to delineate water-oil contacts.Fil: Zyserman, Fabio Ivan. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Monachesi, Leonardo Bruno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Thompson, A. H.. No especifíca;Fil: D'Biassi, T.. YPF - Tecnología; ArgentinaFil: Jouniaux, L.. Université de Strasbourg; FranciaFil: Gauzellino, P.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; Argentin
An analytical solution to assess the SH seismoelectric response of the vadose zone
No full textInternational audienceWe derive an analytical solution of the seismoelectric conversions generated in the vadose zone, when this region is crossed by a pure shear horizontal (SH) wave. Seismoelectric conversions are induced by electrokinetic effects linked to relative motions between fluid and porous media. The considered model assumes a 1D soil constituted by a single layer on top of a half-space in contact at the water table, and a shearing force located at the earth's surface as the wave source. The water table is an interface expected to induce a seismoelectric interfacial response (IR). The top layer represents a porous rock in which porous space is partially saturated by water and air, while the half-space is completely saturated with water, representing the saturated zone. The analytical expressions for the coseismic fields and the interface responses, both electric and magnetic, are derived by solving Pride's equations with proper boundary conditions. An approximate analytical expression of the solution is also obtained, which is very simple and applicable in a fairly broad set of situations. Hypothetical scenarios are proposed to study and analyse the dependence of the electromagnetic fields on various parameters of the medium. An analysis of the approximate solution is also made together with a comparison to the exact solution. The main result of the present analysis is that the amplitude of the interface response generated at the water table is found to be proportional to the jump in the electric current density, which in turn depends on the saturation contrast, poro-mechanical and electrical properties of the medium and on the amplitude of the solid displacement produced by the source. This result is in agreement with the one numerically obtained by the authors, which has been published in a recent work. We also predict the existence of an interface response located at the surface, and that the electric interface response is several orders of magnitude bigger than the electric coseismic field, whereas it is the opposite using compressional waves as shown by theoretical and experimental results. This fact should encourage the performance of field and laboratory tests to check the viability of SHTE seismoelectrics as a near surface prospecting/monitoring tool
A reduced order approach for probabilistic inversions of 3-D magnetotelluric data I: general formulation
No full textThis is a pre-copyedited, author-produced PDF of an article accepted for publication in Geophysical journal international following peer review. The version of record Manassero, M. [et al.]. A reduced order approach for probabilistic inversions of 3-D magnetotelluric data I: general formulation. "Geophysical journal international", Desembre 2020, vol. 223, núm. 3, p. 1837-1863 is available online at: https://academic.oup.com/gji/article-abstract/223/3/1837/5900140?redirectedFrom=fulltext.Peer ReviewedPostprint (author's final draft
Un método de máxima entropía para el análisis de una mezcla de tierras raras
No full textSe propone un método basado en el Principio de Máxima Entropía para analizar mezclas de Tierras Raras en base a medidas magnéticas. El algoritmo está especialmente diseñado para tener en cuenta el error de los datos y la restricción de la positividad de la solución buscada. SUMMARY A method based upon the Maximum Entropy Principle is here developed in order to analyze Rare Earth mixtures with the help of magnetic measurements. The proposed algorithm is so devised as to take into account both experimental errors and the requirement of posivity of the solution.Peer Reviewe
Un método de máxima entropía para el análisis de una mezcla de tierras raras
No full textSe propone un método basado en el Principio de Máxima Entropía para analizar mezclas de Tierras Raras en base a medidas magnéticas. El algoritmo está especialmente diseñado para tener en cuenta el error de los datos y la restricción de la positividad de la solución buscada. SUMMARY A method based upon the Maximum Entropy Principle is here developed in order to analyze Rare Earth mixtures with the help of magnetic measurements. The proposed algorithm is so devised as to take into account both experimental errors and the requirement of posivity of the solution.Peer Reviewe
