Preprints
https://doi.org/10.22541/essoar.168869169.98437293/v3
https://doi.org/10.22541/essoar.168869169.98437293/v3
24 Nov 2023
 | 24 Nov 2023

Crustal Softening at Propagating Rift Tips, East Africa

Folarin Kolawole and Rasheed Ajala

Abstract. We investigate the upper-crustal structure of the Rukwa-Tanganyika Rift Zone, East Africa, where earthquakes anomalously cluster at the northwestern tip of the Rukwa Rift, the eastern tip of the Mweru-Wantipa Rift, and along the Tanganyika Rift axis. The current rift tips host distributed faulting in exposed basement with little sedimentation. Here, we invert earthquake P and S travel times to produce three-dimensional upper-crustal velocity models for the region. The resulting models reveal the occurrence of anomalously high Vp/Vs ratios that extend from the surface down to ca. 10 km at the tip zones of the Rukwa and Mweru-Wantipa rifts. The spatial association of distributed faulting, upper-crustal seismicity, and thermal anomalies with the high Vp/Vs ratios suggest a weakened crust below the rift tips’ flexural zone. We propose an ongoing strain localization and crustal softening at the rift tips that is accommodated by brittle damage from bending strain, and potentially compounded by hydrothermal weakening. This setting represents a precursory phase that may initiate unilateral rift tip propagation.

Folarin Kolawole and Rasheed Ajala

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2628', Anonymous Referee #1, 26 Dec 2023
    • AC2: 'Reply on RC1', Folarin Kolawole, 01 Mar 2024
  • RC2: 'Comment on egusphere-2023-2628', Anonymous Referee #2, 28 Dec 2023
    • AC3: 'Reply on RC2', Folarin Kolawole, 01 Mar 2024
  • EC1: 'Comment on egusphere-2023-2628', Frank Zwaan, 17 Jan 2024
    • AC1: 'Reply on EC1', Folarin Kolawole, 01 Mar 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2628', Anonymous Referee #1, 26 Dec 2023
    • AC2: 'Reply on RC1', Folarin Kolawole, 01 Mar 2024
  • RC2: 'Comment on egusphere-2023-2628', Anonymous Referee #2, 28 Dec 2023
    • AC3: 'Reply on RC2', Folarin Kolawole, 01 Mar 2024
  • EC1: 'Comment on egusphere-2023-2628', Frank Zwaan, 17 Jan 2024
    • AC1: 'Reply on EC1', Folarin Kolawole, 01 Mar 2024
Folarin Kolawole and Rasheed Ajala

Data sets

Supplementary Document for Crustal Softening at Propagating Rift Tips, East Africa Folarin Kolawole and Rasheed Ajala https://drive.google.com/file/d/1riHkK223wrQ39Ix7gdcnki58BRAxLqUV/view?usp=sharing

Reproducibility material for crustal softening at propagating rift tips Rasheed Ajala and Folarin Kolawole https://doi.org/10.5281/zenodo.8302196

Folarin Kolawole and Rasheed Ajala

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Short summary
We investigate the upper-crustal structure of the Rukwa-Tanganyika Rift Zone, East Africa, where earthquakes anomalously cluster at the tips and axes of active rifts. Rift tip earthquakes collocate with a zone of distributed faulting in exposed crystalline basement. Seismic velocity structure reveals ~10 km-deep zones of anomalously high Vp/Vs ratios at the rift tips representing localized mechanical weakening of the crust, interpreted to be a precursory phase that initiates rift propagation.