Mapping of surface deformation associated with the 5.2 magnitude Stilfontein earthquake of 3 April 2017 using radar interferometry

Abstract

This paper presents surface deformation associated with the 5.2 magnitude Stilfontein earthquake of 3 April 2017 using Sentinel-1 data. Analysis involved calculation of vertical displacement for two situations (unmasked and masked with a layer of coherence ≥0.6). The displacement for the unmasked situation ranged from −21 mm to +49 mm whereas with higher coherence of ≥0.6 it ranged from −18 mm to 45 mm. Major positive displacements of 32–45 mm observed in the KOSH region whereas negative displacements of −15 mm to −28 mm observed in the northern, north-eastern, north-western and south-western part of the image. Comparison of vertical displacement with geology indicated that the areas of high positive deformation or uplifts were in the central portion of the image underlain by the geological units of Malmani Subgroup, Rietgat Formation, Klipriviersberg Group, Dominion Group, Hospital Hill Subgroup, Allanridge Formation and Volksrust Formation. Areas of high negative deformation or subsidence are confined to the northern and north-eastern region underlain by Malmani Subgroup and north-western region underlain by Kameeldoorns Formation and south-western region underlain by Allanridge Formation. An attempt to compare the deformation and vertical displacement with isoseismal map revealed similarity/matching of higher surface deformation areas with the shapes and values of high value isoseismal contours. No major faults were seen at or near the epicentre of the earthquake. The surface deformation distribution associated with the occurred earthquake will help to identify possible areas of major deformation, if earthquake of same magnitude and depth of origin occurs in the same area in future.