On the Origin of Orphan Tremors and Intraplate Seismicity in Western Africa

T Olugboji,A A Adepelumi,Yingping Lu,Manoochehr Shirzaei,F Kolawole

doi:10.3389/feart.2021.716630

Abstract

On September 5–7, 2018, a series of tremors were reported in Nigeria’s capital city, Abuja. These events followed a growing list of tremors felt in the stable intraplate region, where earthquakes are not expected. Here, we review available seismological, geological, and geodetic data that may shed light on the origin of these tremors. First, we investigate the seismic records for parent location of the orphan tremors using a technique suitable when a single-seismic station is available such as the Western Africa region, which has a sparse seismic network. We find no evidence of the reported tremors within the seismic record of Western Africa. Next, we consider the possibility of a local amplification of earthquakes from regional tectonics, reactivation of local basement fractures by far-field tectonic stresses, post-rift crustal relaxation, landward continuation of oceanic fracture zones, or induced earthquakes triggered by groundwater extraction. Our assessments pose important implications for understanding Western Africa’s intraplate seismicity and its potential connection to tectonic inheritance, active regional tectonics, and anthropogenic stress perturbation.

Highlights

On September 5–7, 2018, a series of low-magnitude tremors hit Nigeria’s capital city in Mpape, Abuja (Government Report, 2018)
Based on the available InSAR analysis, we find the strongest support for the hypotheses that these events were triggered by groundwater extraction (H-IV)
While other hypotheses cannot be ruled out completely for the case study presented here, we point out that more work is needed to establish a better understanding of the potential connections between inherited basement structure, active regional tectonics, and anthropogenic stress perturbations

Summary

Introduction

On September 5–7, 2018, a series of low-magnitude tremors hit Nigeria’s capital city in Mpape, Abuja (Government Report, 2018) These events followed a series of earthquakes felt in the region since 1933, a stable, intraplate setting, otherwise not being earthquake-prone (Akpan and Yakubu, 2010; Akpan et al, 2014; Tsalha et al, 2015). Nigeria is located in the southern part of the Neoproterozoic Trans-Saharan Mobile Belt, separating the Archean West African Craton, Congo Craton, and the Archean-Proterozoic Sahara Metacraton Within this mobile belt, a large continent-scale system of elongate rift basins (aulacogens) developed during the Cretaceous, among which is located the Benue Trough on whose flank the Abuja city is located (Figure 1A). Note that in the context of this paper, the term “tremor” is used in its general meaning with no particular emphasis on the processes that are attributed to a tremor activity, such as fluid migration and slow slip events, observed in some volcanic and tectonic settings (Rogers and Dragert, 2003; McCausland et al, 2005; Nadeau and Dolenc, 2005; Wech et al, 2012; Montgomery-Brown et al, 2013)

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Results

Discussion

Conclusion