Integrated geophysical investigation of recent earth tremors in Nigeria using aeromagnetic and gravity data.

Abstract

Understanding the tectonics at active sites of recent seismic activities in Nigeria is fundamental towards disaster mitigation and emergency planning. We apply geophysical techniques of gravity and magnetic methods to investigate crustal depths, subsurface geologic faults and fractures, and the overall subsurface interaction at Mpape region and environs. Estimated depths to the bottom of magnetic crust (basal depths) range between 11.0 and 11.4km at the Mpape region and decrease further southward towards Guabe town. This signifies the depth range of the active crust within the region. Comparative deeper basal depths (15.0-16.2km) were obtained at locations farther from Mpape-Guabe towns at Nasarawa, Rubochi, and Fuka regions, showing a more stable region away from Mpape region. Computed Moho depths from gravity data show deeper depths at the Mpape region (~ 34.1km) suggesting that the active crust exists in the upper crust. Two-dimensional modeling analysis along a profile taken across the Mpape region shows a conspicuous subsurface basement intrusion at the Mpape region with deep faults and fractures reaching depths of 7-14km. Shallow basal depths at the Mpape region resulting from significant subsurface intrusion and concentrated subsurface faults at the intruded region may be responsible for the instability of the Mpape region. The most affected area is located within the Mpape-Guabe towns. We recommend the establishment of seismic monitoring facilities in this area for effective monitoring and evaluation.