Aeromagnetic mapping of fault architecture along Lagos–Ore axis, southwestern Nigeria

Abstract

AbstractA seismic wave is released when there is sudden displacement on a fault plane. The passage of this wave along the fault plane or within the lithosphere could result in ground shaking or vibration at the surface of the Earth. To provide a geophysical explanation to this phenomenon, the high-resolution aeromagnetic data of the sedimentary terrain and part of the Basement Complex of Southwestern Nigeria were processed and interpreted to provide fault architecture of the area, which could serve as conduit for the passage of seismic energy in the study area. High-resolution aeromagnetic data along the Lagos–Ore axis are processed for fault mapping in the study area. The reduced-to-equator (RTE) residual aeromagnetic data used were enhanced using the total horizontal derivative (THD) and upward continuation (UC) filtering techniques on Oasis Montaj 6.4.2 (HJ) software. The resultant maps were overlaid and compared with the plotted RTE residual maps for relevant interpretations. Varying signatures of magnetic anomalies are grouped into high (57.9–89.1 nT), intermediate (38.2–57.9 nT), and low (4.0–38.2 nT) magnetic intensities, which are associated with contracting basement rocks features. The obtained lineaments from the THD reveal areas of various deformations such as brittle, which is associated with faults/fractures, and ductile deformation, which is associated with folds of geological features. The faults, as depict by the UC map, reveal different depth ranges of 500–2250 m at the western side and 1,500–1,250 m at the northwestern area of the study. Since it has been on record that September 11, 2009, earth tremor of magnitude 4.4, with the epicenter at Allada, Bennin Republic, 128 km west of Lagos, Nigeria occurred within the study area, it can be inferred that the established geologic fault architecture could be responsible for the hazard and be part or synthetic to the Ifewara-Zungeru fault in Nigeria.