MAGNETIC AND SEISMOLOGICAL INVESTIGATION OF RECENT EARTH TREMOR IN PARTS OF NORTH CENTRAL NIGERIA

Abstract

High resolution aeromagnetic data and Seismological data of parts of North Central Nigeria were analyzed and interpreted with the aim of detecting the source of the recent earth tremors in the area. The study area is bounded by latitude 9. 00o to 10. 00o N and longitude 7.00o to 9.00 o E with an estimated total area of 24, 200km2. The total magnetic intensity (TMI) of the study area was reduced to magnetic equator, Analytic signal and upward continuation techniques was applied to the RTE map. The TMI and the RTE map are characterized with high and low magnetic signature with the intensity ranging from 3377.1to 33460.3 nT and 33094.659 to 32908.968 respectively with dominants structures trending NE-SW. Upward continuation techniques has been used in this study to locate prominent deep-seated anomalies, at 5 km the fault is deep-seated. The analytic signal reveals variations in the amplitude of the magnetic susceptibility of the rocks within the study area. Structural analyses (1VD, Horizontal, Tilt and CET derivative) were used in this study to locate the position of magnetic lineament (faults or fractures) within the area. Four major trends were observed NE-SW, NW-SE, E-W and NNE-SSW. The dominant trends are NW-SE and NNE-SSW within this area. The magnitude, epicenter and time of occurrence were determined using Seismological method. The origin time for the first event of Kwoi earthquake occurred on 11th September, 2016 at 12:28:16.50 seconds, the second event occurred on 12th September, 2016 at 03:10:48.80 seconds and the third event occurred on 12th September, 2016 at 03:11:20.00 seconds respectively. Magnitude of kwoi earth tremor was determined for three events, the first has a local magnitude of 2.8 and moment magnitude of 3.1, second event has local magnitude of 2.7 and moment magnitude of 3.0 and the third event has a local magnitude of 3.1 and moment magnitude of 3.1. The first and third event has a moment magnitude of 3.1. The epicentre was estimated to occurred at latitude 9.570oN and longitude 8.070oE for first event, latitude 9.640oN and longitude 8.180oE for second event and the third event at latitude 9.590oN and longitude 8.130oE. The magnitude of Abuja earth tremor was estimated with a main shock of local magnitude of 3.0, moment magnitude is 2.6. First and second aftershock, with a moment magnitude of 2.5 and local magnitude of 2.6, and a moment magnitude of 2.2 and local magnitude of 2.5. The epicenter for the first aftershock to be located at latitude 9.0339oN and longitude 7.5008oE. The Second aftershock was located at latitude 9.1620oN and longitude 7.4014oE. The main shock was located at latitude of 9.139oN and longitude 7.594oE. The origin time for the main shock of Abuja earthquake occurred in September and October 2018 at 5:11:32.60 seconds, the first aftershock occurred at 6:16:17.80 seconds and the second aftershock occurred at 7:12:18.40 seconds respectively. The Lineament map was superimposed on the epicenter map to identify the fault that coincides with the epicenter. Fault F5, F6 and F8 coincides with some of the epicenters corresponding to areas around Jaba, ZangonKataf, and part of Municipal area council. Fault F4 and F8 coincides with epicenter at Jema’a and Municipal area council, these are areas affected by earth tremor in 2016 and 2018. Therefore, the earth tremor activities within the study area are as a result of the effect of the emergence of these near surface faults.