Geophysical evidence for crustal and mantle weak zones controlling intra-plate seismicity – the 2017 Botswana earthquake sequence

The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above. ; Large earthquakes away from plate boundaries pose a significant threat to human lives and infrastructure, but such events typically occur on previously unknown faults. Most cases of intra-plate seismicity result from compression related to far-field plate boundary stresses. The April 2017 MW 6.5 earthquake in central Botswana, and subsequent events, occurred in a region with no previously known large earthquakes, occurred away from major present day tectonic activity, and accommodate extension rather than compression. Here, we present results from an integrated geophysical study that suggests the recent earthquakes may be a sign of future activity, controlled by the collocation of a weak upper mantle and weak crustal structure, between otherwise strong Precambrian blocks. Magnetotelluric data highlights Proterozoic continent accretion structure within the region, and shows that recent extension and seismicity occurred along ancient thrust faults within the crust. Our seismic velocity and resistivity models suggest a weak zone in the uppermost mantle, that does not persist to greater depths, and is therefore unlikely to represent mantle upwelling. The Botswana events may therefore be indicative of top-down extension as a response to large scale extensional forces ; In addition to the funding and logistical support provided by SAMTEX consortium members (Council for Geoscience, Geological Surveys Botswana and Namibia, De Beers Group Services, Rio Tinto Exploration, and BHP Billiton), this work was also supported by research grants from National Science Foundation's Continental Dynamics program (USA, EAR-0309584 and EAR-0455242), the Department of Science and Technology, Republic of South Africa, and Science Foundation Ireland (Ireland, grant 05/RFP/GEO001). ; Peer-reviewed ; Post-print