Stress transfer and poroelasticity associated to major earthquakes in Africa

Abstract

This study focuses on the stress transfer using the Coulomb Failure Function (CFF) modeling and related poroelastic effect of four major earthquake sequences that occurred in different active zones of Africa: the May to July 1990 Sudan earthquake sequence, the May 2018 to June 2019 Mayotte-Comores earthquake swarm sequence, the 1980–2003 El Asnam-Zemmouri (Algeria) earthquake sequence, and the 1994–2016 Al Hoceima (Morocco) earthquake sequence. We observe the relationship between the stress transfer caused by mainshock fault ruptures and the post-seismic deformation controlled by the aftershock distribution. Based on other case studies, our hypothesis is that all seismic sequences are apparently controlled by the increase in pore fluid pressure caused by co-seismic phase and fluid-drained short-term post-seismic response. The poroelastic properties of any seismogenic zone appear to depend on the undrained and drained fluid conditions. The comparison between the 1990 Sudan sequence and the 1994–2016 Al Hoceima (Morocco) stress modeling shows that for most sequences the poroelastic response of the first mainshock play an important role in the occurrence of the second mainshock. Similar observations can be made for the 2018–2019 Mayotte-Comores and the 1980–2003 El Asnam-Zemmouri (Algeria) earthquake sequences. By comparing the case studies, we find that the value of fluid diffusivity controls the timing of earthquake sequences (e.g., more than three times larger between the Al Hoceima and Sudan earthquakes). The constraint of fault interactions with CFF modeling and fluid diffusivity allows a better estimate of the seismic hazard assessment.