Continental rifting is a fundamental component of plate tectonics. Recent studies have highlighted the importance of magmatic activity in accommodating extension during late-stage rifting, yet the mechanisms by which crustal thinning occurs are less clear. The Red Sea rift in Northern Afar presents an opportunity to study the final stages of continental rifting as these active processes are exposed subaerially. Between February 2011 and February 2013 two seismic networks were installed in Ethiopia and Eritrea. We locate 4,951 earthquakes, classify them by frequency content, and calculate 31 focal mechanisms. Results show that seismicity is focused at the rift axis and the western marginal graben. Rift axis seismicity accounts for ∼64% of the seismic moment release and exhibits a swarm-like behavior. In contrast, seismicity at the marginal graben is characterized by high-frequency earthquakes that occur at a constant rate. Results suggest that the rift axis remains the primary locus of seismicity. Low-frequency earthquakes, indicative of magmatic activity, highlight the presence of a magma complex ∼12 km beneath Alu-Dalafilla at the rift axis. Seismicity at the marginal graben predominantly occurs on westward dipping, antithetic faults. Focal mechanisms show that this seismicity is accommodating E-W extension. We suggest that the seismic activity at the marginal graben is either caused by upper crustal faulting accommodating enhanced crustal thinning beneath Northern Afar or as a result of flexural faulting between the rift and plateau. This seismicity is occurring in conjunction with magmatic extension at the rift axis, which accommodates the majority of long-term extension.
|Original language||English (US)|
|Number of pages||18|
|Journal||Journal of Geophysical Research: Solid Earth|
|State||Published - Mar 1 2018|
Bibliographical noteKAUST Repository Item: Exported on 2022-06-08
Acknowledged KAUST grant number(s): OSR-2015-CRG4-2643
Acknowledgements: We thank SEIS-UK for use of the instruments and their computing facilities. The facilities of SEIS-UK are supported by the Natural Environment Research Council (NERC) under agreement R8/H10/64. F. I. K. is funded through NERC studentship NE/L002531/1 and a grant to GSNOCS from Roy Franklin OBE. D. K. is supported by NERC grant NE/L013932 and grant OSR-2015-CRG4-2643 from King Abdullah University of Science and Technology. Funding for fieldwork is from BHP Billiton. B. G. is funded through a PhD scholarship by the University of Bristol and Engineering and Physical Sciences Research Council (EPSRC): grant number DTG EP/L504919/1). C.E. and M. B. were supported by a grant from Statoil. We also acknowledge assistance from Addis Ababa University and the Afar National Regional State Government. The catalogue of earthquakes located and used in this study is provided in the supporting information. We wish to thank two anonymous reviewers, and the Associate Editor Martha Savage, whose comments helped to improve the paper.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.