Brittle strain regime transition in the Afar depression: Implications for fault growth and seafloor spreading

Numerical and analogue models of fault-population evolution suggest that we should see a frequency-size transition from power law to exponential as br ittle strain within a region increases. We now observe this transition in c ontinental rift faults in the Afar region, Ethiopia and Djibouti. Furthermo re, we observe that this strain transition is accompanied by a plateau in f ault density and an increase in the displacement:length ratio of faults wit h increasing brittle strain. Once faults reach a critical density, stress s hadows of nearby faults inhibit fault nucleation and restrict tip propagati on. However, pinned faults continue to accommodate extension by accumulatin g more displacement, thus leading to higher displacement:length ratios in t he higher strain regime. This strain regime transition is important to unde rstanding the physics of fault growth and may also be important to rift loc alization and the development of plate boundaries.