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Mapping of Surface Deformation and Displacement Associated with the 6.5 Magnitude Botswana Earthquake of 3 April 2017 Using DInSAR Analysis
Corresponding Author(s) : Abraham Thomas
Geomatics and Environmental Engineering,
Vol. 14 No. 4 (2020): Geomatics and Environmental Engineering
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.
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References
USGS: M 6.5 – 132 km WSW of Moijabana, Botswana. USGS, 2017. https://earthquake.usgs.gov/earthquakes/eventpage/us10008e3k#executive [access: 27.09.2018].
Chida D.: The earthquake was natural. Geoscience Institute. The Voice Newspaper Botswana, April 4, 2017. https://thevoicebw.com/earthquake-natural-geoscience-institute/ [access: 27.09.2018].
Gardonio B., Jolivet R., Calais E., Leclère H.: The April 2017 Mw 6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids. Geophysical Research Letters, vol. 45 (17), 2018, pp. 8886–8896. https://doi.org/10.1029/2018gl078297.
Jo Min‑Jeo, Hyung‑Sup Jung, Sung‑Ho Chae: Advances in three‑dimensional deformation mapping from satellite radar observations: application to the 2003 Bam earthquake. Geomatics, Natural Hazards and Risk, vol. 9 (1), 2018, pp. 678–690. https://doi.org/10.1080/19475705.2018.1473293.
Xu G., Xu C., Yangmao W.: Sentinel‑1 observation of the 2017 Sangsefid earthquake, northeastern Iran: Rupture of a blind reserve‑slip fault near the Eastern Kopeh Dagh. Tectonophysics, vol. 731–732, 2018, pp. 131–138. https://doi.org/10.1016/j.tecto.2018.03.009.
Jung H.S., Lu Z., Won J.S., Poland M.P., Miklius A.. Mapping three‑dimensional surface deformation by combining multiple‑aperture interferometry and conventional interferometry: Application to the June 2007 eruption of Kilauea volcano, Hawaii. IEEE. Geoscience and Remote Sensing Letters, vol. 8 (1), 2011, pp. 34–38. https://ieeexplore.ieee.org/document/5503996 [access: 12.09.2020].
Bayer B., Simoni A., Mulas M., Corsini A., Schmidt D.: Deformation responses of slow moving landslides to seasonal rainfall in the Northern Apennines, measured by InSAR. Geomorphology, vol. 308, 2018, pp. 293–306. https://doi.org/10.1016/j.geomorph.2018.02.020.
Amos J.: Sentinel maps North Korean nuclear blast aftermath. BBC, April 21, 2016. http://www.bbc.com/news/science-environment-36103812 [access: 28.03.2019].
Kolawole F., Atekwana E.A., Malloy S., Stamps D.S., Grandin R., Abdelsalam M.G., Leseane K., Shemang E.M.: Aeromagnetic, gravity, and Differential Interferometric Synthetic Aperture Radar analyses reveal the causative fault of the 3 April 2017 Mw 6.5 Moiyabana, Botswana, earthquake. Geophysical Research Letters, vol. 44 (17), 2017, pp. 8837–8846. https://doi.org/10.1002/2017gl074620.
Albano M., Polcari M., Bignami C., Moro M., Saroli M., Stramondo S.: Did Anthropogenic Activities Trigger the 3 April 2017 Mw 6.5 Botswana Earthquake? Remote Sensing, vol. 9 (10), 2017, pp. 1028 (1–12). https://doi.org/10.3390/rs9101028.
Materna K., Wei S., Wang X., Heng L., Wang T., Chen W., Salman R., Bürgmann R.: Source characteristics of the 2017 Mw 6.4 Moijabana, Botswana earthquake, a rare lower‑crustal event within an ancient zone of weakness. Earth and Planetary Science Letters, vol. 506, 2019, pp. 348–359. https://doi.org/10.1016/j.epsl.2018.11.007.
ESA: Interferometric Wide Swath, User Guides, Sentinel‑1 SAR. ESA, 2016. https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/acquisition-modes/interferometric-wide-swath [access: 27.09.2018].
Massonnet D., Rossi M., Carmona C., Adragna F., Peltzer G., Feigl K., Rabaute T.: The displacement of the Landers earthquake mapped by radar interferometry. Nature, vol 364 (6433), 1993, pp. 138–142.
Veci L.: TOPS Interferometry Tutorial. Sentinel‑1 Toolbox. Array Systems Computing Inc. and ESA, 2015. http://step.esa.int/docs/tutorials/S1TBX%20Stripmap%20Interferometry%20with%20Sentinel-1%20Tutorial.pdf [access: 27.09.2018].
Chen C.W., Zebker H.A.: Network approaches to two‑dimensional phase unwrapping: intractability and two new algorithms. Journal of the Optical Society of America A, vol. 17 (3), 2000, pp. 401–414. https://doi.org/10.1364/JOSAA.17.000401.
Stanford: SNAPHU: Statistical‑Cost, Network‑Flow Algorithm for Phase Unwrapping. Stanford University, 2003. http://web.stanford.edu/group/radar/softwareandlinks/sw/snaphu/ [access: 27.09.2018].
Walter D.: Surface subsidence monitoring with NEST. Tutorial – SAR Interferometry. Institute of Geotechnical Engineering and Mine Surveying, TU Clausthal, 2014. https://saredu.dlr.de/unit/insar_deformation [access: 27.09.2018].
Meghraoui M., Amponsah P., Ayadi A., Ayele A., Ateba B., Bensuleman A., Delvaux D. et al.: The seismotectonic map of Africa. Episodes, vol. 39 (1), 2016, pp. 9–18. https://doi.org/10.18814/epiiugs/2016/v39i1/89232.
Midzi V., Saunders I., Manzunzu B., Kwadiba M.T., Jele V., Mantsha R., Marimira K.T. et al.: The 03 April 2017 Botswana M6.5 earthquake: Preliminary results. Journal of African Earth Sciences, vol. 143, 2018, pp. 187–194. https://doi.org/10.1016/j.jafrearsci.2018.03.027.