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During the August 1989 sequence of earthquakes beneath the Dobi graben in Central Afar, principal events (including 10 shocks with M L ≥5.5) propagated ∼50 km north‐westwards in ∼50 h. The sequence is analyzed in terms of triggering by propagation of a critical pore pressure wave in a compressible fluid through a fractured medium. The macroscopic fluid diffusion tensor D in the crust beneath the graben is estimated. Its principal eigenvector strikes ∼N115°E nearly parallel to the graben axis. With a value , it is about 10 times larger than the other two, consistent with fissure anisotropy in the graben. The order of magnitude of the permeability (∼10 −8 m²) is compatible with characteristic fissure widths ranging from 1 mm to 3 cm. Estimating such parameters in other extensional regions might help to understand better the temporal evolution of seismic swarms.
Noir et al. (Mon,) studied this question.