Aeromagnetic, gravity, and Differential Interferometric Synthetic Aperture Radar analyses reveal the causative fault of the 3 April 2017 M_w 6.5 Moiyabana, Botswana, earthquake

Abstract

On 3 April 2017, a Mw 6.5 earthquake struck Moiyabana, Botswana, nucleating at >20 km focal depth within the Paleoproterozoic Limpopo‐Shashe orogenic belt separating the Archean Zimbabwe and Kaapvaal Cratons. We investigate the lithospheric structures associated with this earthquake using high‐resolution aeromagnetic and gravity data integrated with Differential Interferometric Synthetic Aperture Radar (DInSAR) analysis. Here we present the first results that provide insights into the tectonic framework of the earthquake. The ruptured fault trace delineated by DInSAR aligns with a distinct NW striking and NE dipping magnetic lineament within the Precambrian basement. The fault plane solution and numerical modeling indicate that the cause of the earthquake was 1.8 m displacement along a NW striking and NE dipping normal fault, rupturing at 21–24 km depth. We suggest that this seismic event was due to extensional reactivation of a crustal‐scale Precambrian thrust splay within the Limpopo‐Shashe orogenic belt.

Did Anthropogenic Activities Trigger the 3 April 2017 Mw 6.5 Botswana Earthquake?

“…Indeed, the residuals in the simulated LoS displacements are lower than 1 cm in the area affected by the maximum displacement. The retrieved fault position, geometry and mechanism fairly agree with the CMT solution and with a previous forward modelling of InSAR data performed by Kolawole et al [4] ( Table S1). On the contrary, the estimated resultant slip and rake (approximately 2.7 m and −131 • ) slightly differ from previous inversion of InSAR data [4], thus identifying a predominant right-lateral dislocation component.…”

“…The retrieved fault position, geometry and mechanism fairly agree with the CMT solution and with a previous forward modelling of InSAR data performed by Kolawole et al [4] ( Table S1). On the contrary, the estimated resultant slip and rake (approximately 2.7 m and −131 • ) slightly differ from previous inversion of InSAR data [4], thus identifying a predominant right-lateral dislocation component. It is noteworthy that Kolawole et al [4] performed the inversion of InSAR data by fixing the fault rake while we allowed the rake to vary between 0-360 • , according to the selected bounds for the strike and dip slip components ( Table 1).…”

“…Indeed, the earthquake epicenter is located in an extensional area (Figure 6a), where a new rifting zone is developing [30]. Moreover, the retrieved fault geometry (i.e., strike and dip) is consistent with the tectonic structures inferred from 3D aeromagnetic and gravimetric data [4] (Figure 6b). …”

“…Thus, the distance at depth between production wells and the retrieved earthquake source is greater than 20 km. (a), showing the location of the retrieved fault geometry respect to the Lesedi project permits (http://tlouenergy.com/lesedi-cbm-project) and the tectonic structures inferred from 3D aeromagnetic and gravity data [4]. The colored map shows the LoS ground displacements from InSAR data (see Figure 2b).…”

“…org) and the preliminary inversion results of teleseismic body waves (http://geoscope.ipgp.fr/index. php/en/catalog/earthquake-description?seis=us10008e3k) [3] and InSAR data [4] indicate a normal faulting mechanism located at a depth greater than 20 km. (Table S1).…”