Compatibility of Electromagnetic (EM) Method and Geospatial Analysis for Identifying the Vulnerable Building Zonation in Coastline Area of Ado-Odo Ota, Ogun State, Nigeria

Abstract

Abstract Collapsing of building incidents have been reported all over the world and seems to be commonespecially in sedimentary terrain of the coastal plain sand of Ado-Odo Ota which has the same subsurface features as the Lagos that experience regular building collapse. This building collapse is attributed to several causes. The reasons that have been identified, have added little or no impact on reducing this environmental disaster. This study presents the strength of emerging and existing geophysical tools for near-surface structural studies. The aim is to reveal the recent technical development on improving field surveys to minimize building collapse. Data acquisition using electromagnetic (EM) methods which are known for fast mapping of near-surface spatial variation as well as obtaining the subsurface vertical variation in electrical conductivity was adopted. The acquired spatial and attribute data was introduced in a GIS environment with different thematic vectors/layers created by digitizing the satellite image of the study area. The GIS digitizing was to geographically trace the acquired data with accurate coordinates from the obtained EM field data with the thematic layer representing the features such as weak zone and competence zones that can hold buildings. A transverse was taken in a strategic positions considering the regional features with 10 m spacing to cover the marked stations. It revealed the layer depths range from 0.37 to 1.64 m with the much competence layer found to be about 1.64 mbeyond which may be the thick clay Ilaro formation that underlies the recent formation. The weathered shear zone at the depth of 0.37 m may be the recent lithoral deposits which is geotechnically and geologicallyunstable and proximity to active faults of ruptured geomorphology of the building zonation.