Seismic and aseismic deformation in the Danakil Depression, East Africa and Corinth Rift, Greece: Magma-rich vs magma-poor rift extension

The mechanisms accommodating extension in magma-rich and magma-poor rifts likely differ, with magmatic intrusion (largely aseismic) potentially dominating magma-rich rifts and faulting (seismic deformation) thought to accommodate most extension in magma-poor rifts. We compared the seismic and aseismic deformation occurring in the Danakil Depression, East Africa (magma-rich) and Corinth Rift, Greece (magma-poor) to test this hypothesis and improve understanding of extension in end-member rifts. The seismic moment release across both rifts was determined using NEIC catalogue earthquake data (from 1950 to 2023). In the Danakil Depression, seismic moment release is highest at the rift margins and sections of the rift axis with reduced magmatism. Seismic moment release is greatest across the eastern part of the Corinth Rift. Regional geodetic extension data were used to calculate the changing geodetic moment rates along both rifts. The ratio between the seismic and geodetic moment rates (S/G) was calculated for the entire rifts and overlapping zones along each rift. The horizontal component of the seismic moment was extracted to calculate the horizontal seismic/geodetic moment rate ratio (S-h/G). The Danakil Depression and Corinth Rift have S/G of 0.03 and 0.43, and S-h/G of 0.02 and 0.28, respectively, suggesting greater amounts of extension being accommodated by faulting in the Corinth Rift. S/G variations along the Danakil Depression are consistent with geological indicators of along-rift variations in faulting. Relatively high S/G (similar to 0.1) in the north of the Depression indicates that brittle deformation accommodates a significant amount of extension here, despite being potentially in the final stages of magma-rich break-up. Relatively low S/G (similar to 0.1-0.15) in the west of the Corinth Rift supports the interpretations that aseismic deformation may be significant, potentially on a low-angle detachment at depth. This study confirms our hypothesis that in magma-poor rifts, greater amounts of extension are accommodated by seismic deformation compared with magma-rich rifts.