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Asian Journal of Earth Sciences

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This is an Open Access Journal

Open Access journal
ISSN (Print) 1819-1886 - ISSN (Online) 2152-3509
Published by Science Alert

[51 journals]

Monitoring of GPS Water Vapor Variability During ENSO Events over the Borneo Region
- Abstract: The cycle of El Niño-Southern Oscillation (ENSO) is very crucial to affect the natural climate variability in a particular region. Direct measurement of ENSO cycle and to understand their comprehensive physical mechanism are still difficult for sustainable development. For that purpose, a Precipitable Water Vapor (PWV) derived from a ground-based Global Positioning System (GPS) receiver is proposed. The PWV for the year 2011 gathered from Universiti Malaysia Sabah located in Kota Kinabalu, Malaysia (UMSK) together with two other selected GPS stations centered the Borneo region in pathways of Niño 4 region, named Nanyang Technological University (NTUS) in the Singapore and Manila Observatory (PIMO) in Philippines were analyzed. The GPS PWV was also compared with PWV taken from Radiosonde (RS). The results found a good agreement between GPS PWV and RS PWV with correlation coefficients ranging from 0.6 to 0.8, significantly at the 99% confidence level. PWV at Philippine's station demonstrated a drop about 7.8 mm before the first monsoon and PWV in the whole station look like a bimodal pattern throughout the year. An investigation of ENSO episode in September with weak-to-moderate intensity between PWV and the sea-surface temperature anomaly demonstrated an inverse correlation due to La Niña events. This promising result indicates that during the La Niña event, the PWV is increased when the sea-surface temperatures getting cold and thereby slow down the GPS signals.
  PubDate: 21 March, 2013
Estimation of Magnetic Basement Depths Beneath the Abeokuta Area, South West Nigeria from Aeromagnetic Data Using Power Spectrum
- Abstract: This study presents the result of spectral analysis of aeromagnetic data of Abeokuta area, a basement complex of South-western Nigeria. Aeromagnetic survey is a powerful tool in delineating the regional geology of buried basement terrain. The purpose of magnetic surveying is to investigate the subsurface based on the variation in the observed magnetic field result from the differences in the magnetic properties of the underlying rocks, or in some cases cultural sources. In order to achieve the aim of this study, matched pass filtering operation was performed on digitised aeromagnetic data of the area under consideration to separate magnetic anomalies produce by shallow features and cultural features separated from anomalies produced by deeper geologic unit. Two-dimensional spectral analysis revealed that the magnetic sources are mainly distributed at two levels. The shallow source is depth 0.467 km below ground level is inferred to be due to the intrusions within the region. The deeper sources depth, which is 2.797 km below ground, is attributed to the underlying basement. The mean shallow depth and deeper depth are 0.467 km and 2.797 km, respectively. The shallow depth of 0.467 km might probably due to intrusive within the sediment while deeper depth of 2.797 km is attributed to underlying basement. Variation in magnetic depth values reveals the general trends in the magnetic basement surface.
  PubDate: 21 March, 2013
Geophysical Characterization of Basement Rocks and Groundwater Potentials Using Electrical Sounding Data from Odeda Quarry Site, South-western, Nigeria
- Abstract: This study was carried to characterize the basement rocks and groundwater potentials by delineating the resistivity and overburden thickness of subsurface lithology of Odeda quarry, south-western, Nigeria. Vertical electrical soundings were carried out at fifteen locations using Schlumberger electrode arrangement. The maximum current electrode spread and potential electrode separation were 200 and 5 m, respectively. Data acquired were interpreted using the manual partial curve matching method and a fast computer iteration technique to generate the geoelectric layer of various resistivity values and thicknesses. The geoelectric sections revealed the lithological sequence as: topsoil, weathered layer and fresh bedrock. The overburden coefficient of anisotropy also revealed that, the underlying basement rock is suspected be granite gneiss/granite-schist. The overburden coefficient of anisotropy was calculated for each sounding location and this ranges from 1.00 to 2.30. This was used in delineating the study area into region underlain by granite gneiss (λ between 1.00 and 1.03) and those regions with granite-schist (λ between 1.30 and 2.30) as the underlying basement rocks. At locations where current terminated at the fresh bedrock region, the thicknesses were undetermined. Groundwater potential is presumed to be very low within the study area as outcrops of gneissic rocks dominate the area. Locations where the regolith is of appreciable thickness, the resistivity of the layer suggests a material medium likely composed of clay/sandy clay or clayey sand which are not good aquiferous media from which groundwater could be extracted.
  PubDate: 21 March, 2013

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