Seismic Tomography for Crustal Imaging Beneath Nsukka, Ife, and Kaduna Seismic Stations in Nigeria

Abstract

This study investigates crustal structure beneath the Nsukka, Ife, and Kaduna seismic stations in Nigeria using waveform data from the 11 September 2009 earthquake recorded by the national seismic network. The work applies body-wave phase modelling to examine P- and S-wave propagation and to estimate selected crustal parameters beneath the three recording stations. The analysis used available station coordinates, earthquake source parameters, processed waveform records, and a global crustal velocity model as an initial reference model. Seismic wave arrivals and phase conversions were examined to estimate Moho depth and to derive compressional-wave velocity, shear-wave velocity, and Vp/Vs ratio from slowness values. The results indicate variable crustal thickness beneath the investigated stations, with estimated Moho depths of approximately 35 km beneath Ife, 39 km beneath Kaduna, and 29 km beneath Nsukka. The shallower Moho estimate beneath Nsukka may reflect crustal thinning associated with the sedimentary and tectonic setting of southeastern Nigeria, whereas the deeper estimates beneath Ife and Kaduna are consistent with their basement-complex settings. The 2009 earthquake source depth indicates a shallow crustal event. The derived Vp, Vs, and Vp/Vs values provide preliminary constraints on crustal properties beneath the stations and are broadly useful for improving regional crustal characterisation. The study demonstrates the value of local earthquake waveform records for crustal investigation in Nigeria, while also emphasizing the need for a denser seismic network and a locally calibrated velocity model to improve future seismic hazard assessment and subsurface interpretation.