Fluid flow triggered migration of events in the 1989 Dobi earthquake sequence of Central Afar

During the August 1989 sequence of earthquakes beneath the Dobi graben in Central Afar, principal events (including 10 shocks with M-L greater than or equal to 5.5) propagated similar to 50 km north-westwards in similar to 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 similar to N115 degrees E nearly parallel to the graben axis. With a value (D) over bar xx similar to 2 km(2)/min, it is about 10 times larger than the other two, consistent with fissure anisotropy in the graben. The order of magnitude of the permeability (similar to 10(-8) m(2)) 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.