A M Ekanem
Articles written in Journal of Earth System Science
Volume 125 Issue 7 October 2016 pp 1379-1390
Approximate relationship between frequency-dependent skin depth resolved from geoelectromagnetic pedotransfer function and depth of investigation resolved from geoelectrical measurements: A case study of coastal formation, southern Nigeria
The task involved in the interpretation of Vertical Electrical Sounding (VES) data is how to get unique results in the absence/limited number of borehole information, which is usually limited to information on the spot. Geological and geochemical mapping of electrical properties are usually limited to direct observations on the surface and therefore, conclusions and extrapolations that can be drawn about thesystem electrical characteristics and possible underlying structures may be masked as geology changes with positions. The electrical resistivity study pedotransfer functions (PTFs) have been linked with the electromagnetic (EM) resolved PTFs at chosen frequencies of skin/penetration depth corresponding to the VES resolved investigation depth in order to determine the local geological attributes of hydrogeological repository in the coastal formation dominated with fine sand. The illustrative application of effective skin depth depicts that effective skin depth has direct relation with the EM response of the local source over the layered earth and thus, can be linked to the direct current earth response functions as an aidfor estimating the optimum depth and electrical parameters through comparative analysis. Though the VES and EM resolved depths of investigation at appropriate effective and theoretical frequencies have wide gaps, diagnostic relations characterising the subsurface depth of interest have been established. Thedetermining factors of skin effect have been found to include frequency/period, resistivity/conductivity, absorption/attenuation coefficient and energy loss factor. The novel diagnostic relations and their corresponding constants between 1-D resistivity data and EM skin depth are robust PTFs necessary for checking the accuracy associated with the non-unique interpretations that characterise the 1-D resistivitydata, mostly when lithostratigraphic data are not available.
Volume 127 Issue 3 April 2018 Article ID 0040
The presence of fractures in reservoir rocks causes scattering of seismic wave energy. In this paper, we utilize the finite-difference modelling technique to study these scattering effects to gain more insights into the effects and assess the validity of using anisotropic wave scattering energy as a diagnostic tool to characterize fractured hydrocarbon reservoirs. We use a simplified fractured reservoir model with four horizontal layers with a fractured-layer as the third layer. The fractures are represented by grid cells containing equivalent anisotropic medium by the use of the linear slip equivalent model. Our results showthat the scattered energy, quantified through estimates of the seismic quality factor (Q) is anisotropic, exhibiting a characteristic elliptical (cos 2θ) variations relative to the survey azimuth angle θ. The fracture normal is inferred from the minor axis of the Q ellipse. This direction correlates with the direction of maximum wave scattering. Minimum wave scattering occurs in the fracture strike direction inferredfrom the major axis of the Q ellipse. These results provide more complete insights into anisotropic wave scattering characteristics in fractured media and thus, validate the practical utility of using anisotropic attenuation attribute as an additional diagnostic tool for delineation of fracture properties from seismic
Volume 130 All articles Published: 2 July 2021 Article ID 0134 Research article
The Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) microsatellite-monitored data (IAP and ISL) were employed in investigating pre- (30 days) and post- (10 days) perturbations in ionospheric parameters associated with the
$\bullet$ Use of DEMETER data for earthquake prediction.
$\bullet$ Ionospheric plasma parameters used in detecting seismo-genic induced perturbations.
$\bullet$ Quiet atmospheric geomagnetic perturbations before the earthquake is seismogenically induced.
$\bullet$ Seismo-genic anomalies are promising for short-term earthquake prediction.
Volume 130, 2021
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