Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana

Evidence from magnetotelluric and electrical resistivity tomography imaging

Kelsey Mosley Bufford, Estella A. Atekwana, Mohamed G. Abdelsalam, Elijah Shemang, Eliot A. Atekwana, Kevin Mickus, Moikwathai Moidaki, Motsoptse P. Modisi, Loago Molwalefhe

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

We used Magnetotelluric (MT) and Electrical Resistivity Tomography (ERT) to investigate the geometry and nature of faults activity of the Okavango Rift Zone (ORZ) in Botswana, an incipient rift at the southern tip of the Southwestern Branch of the East African Rift System. The ORZ forms a subtle topographic depression filled with Quaternary lacustrine and fluvio-deltaic sediments and is bounded by NE-trending normal faults that are more prominent in the southeastern portion of the rift basin. An MT model from a regional (∼140. km) NW-SE trending MT transect shows that much of the rift basin is underlain by a broad asymmetrical low resistivity anomaly that slopes gently (∼1°) from NW to SE reaching a depth of ∼300. m. This anomaly suggests that faults in the southeastern part of the rift form a NW-dipping border fault zone and that the lacustrine and fluvio-deltaic sediments contain brackish to saline water filling the broad half-graben structure. Furthermore, MT and ERT models from detailed (4-13. km. long) MT transects and resistivity profiles show that one border fault (Thamalakane) and two within-basin faults (Lecha and Tsau) in the southeastern part of the ORZ are characterized by a localized high conductivity anomaly while another border fault (Kunyere) lacks such an anomaly. These localized anomalies are attributed to channelized fresh surface water and saline groundwater percolating through these faults forming "fault zone conductors" and suggest actively displacing faults. The lack of a "fault zone conductor" in the Kunyere fault is interpreted as indicating diminishing displacement on this fault, and that strain was transferred to the Thamalakane fault further to the east. The fluids provide lubricant for the ORZ faults, hence preventing infrequent large magnitude earthquakes, but favoring frequent micro-seismicity.

Original languageEnglish
Pages (from-to)61-71
Number of pages11
JournalJournal of African Earth Sciences
Volume65
DOIs
Publication statusPublished - Apr 9 2012

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rift zone
tomography
electrical resistivity
geometry
tectonics
anomaly
fault zone
transect
basin
lubricant
earthquake magnitude
graben
sediment
normal fault
seismicity
conductivity
surface water
groundwater
fluid

All Science Journal Classification (ASJC) codes

  • Geology
  • Earth-Surface Processes

Cite this

Bufford, Kelsey Mosley ; Atekwana, Estella A. ; Abdelsalam, Mohamed G. ; Shemang, Elijah ; Atekwana, Eliot A. ; Mickus, Kevin ; Moidaki, Moikwathai ; Modisi, Motsoptse P. ; Molwalefhe, Loago. / Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana : Evidence from magnetotelluric and electrical resistivity tomography imaging. In: Journal of African Earth Sciences. 2012 ; Vol. 65. pp. 61-71.
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Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana : Evidence from magnetotelluric and electrical resistivity tomography imaging. / Bufford, Kelsey Mosley; Atekwana, Estella A.; Abdelsalam, Mohamed G.; Shemang, Elijah; Atekwana, Eliot A.; Mickus, Kevin; Moidaki, Moikwathai; Modisi, Motsoptse P.; Molwalefhe, Loago.

In: Journal of African Earth Sciences, Vol. 65, 09.04.2012, p. 61-71.

Research output: Contribution to journalArticle

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T1 - Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana

T2 - Evidence from magnetotelluric and electrical resistivity tomography imaging

AU - Bufford, Kelsey Mosley

AU - Atekwana, Estella A.

AU - Abdelsalam, Mohamed G.

AU - Shemang, Elijah

AU - Atekwana, Eliot A.

AU - Mickus, Kevin

AU - Moidaki, Moikwathai

AU - Modisi, Motsoptse P.

AU - Molwalefhe, Loago

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