Mapping of Surface Deformation and Displacement Associated with the 6.5 Magnitude Botswana Earthquake of 3 April 2017 Using DInSAR Analysis

Abstract

The DInSAR analysis was performed for mapping surface deformation and displacement associated with the 6.5 magnitude Botswana earthquake of 3 April 2017 using Sentinel‑1 data and SNAP. The analyses involved: coregistration of SAR images, interferogram formation, debursting, merging of sub‑swaths, topographic phase removal, phase filtering, phase unwrapping, orthorectification and calculation of vertical displacement for two situations (unmasked and masked with a layer of coherence ≥0.6). The vertical displacement for the unmasked situation ranged from −122 mm to +136 mm whereas in the masked layer it ranged from −84 mm to +122 mm. Negative surface deformation (subsidence) is seen in the epicentre region and eastern, north‑eastern, northern areas of the image whereas major positive surface deformations (uplift) are seen in the south‑western, western and north‑western corner part. Comparison of displacements with geology revealed that major deformation occurred in the Karoo basalts and lesser surface deformation has occurred in the Lebung Group rocks of the northern, NE and SW region. The elongated shape of deformation near the epicentre and positive vertical displacement seen towards the SW of the epicentre and negative vertical displacement seen towards NE of the epicentre reveals that the region has undergone uplifting and subsidence on either side of the area close to the epicentre (similar to faulting in a NW or SE direction). The boundaries of the uplift and subsidence regions inferred as long lineaments were digitised as faults. Comparison of the deformation with existing seismotectonic map revealed the existence of some north‑westerly faults seen in the region.

Estimation of Mining-Induced Horizontal Strain Tensor of Land Surface Applying InSAR

“…Therefore, InSAR is now commonly used to assess ground movements caused by natural and anthropogenic phenomena such as seismicity [38], volcano eruptions [39], landslides [40], glacier motions [41], mining activity [42], and tunnelling [43]. The displacements of the land surface using InSAR data are first calculated in the lineof-sight (LOS) direction [44,45]. Determining the values of such movements in different directions necessitates the use of additional satellite data acquisition geometry [46] or physics assumptions about the observed phenomenon [47].…”