UCLA

We present new measurements of the surface deformation associated with the rifting

event of 1978 in the Asal-Ghoubbet Rift, Republic of Djibouti using an optical image

correlation technique. Deformation in the rift associated with the event included the

reactivation of the main bordering faults and the development of numerous open fissures

on the rift floor. We combine these new measurements with ground-based observations

from previous work to constrain a kinematic model of the rift consisting of two bordering

faults reaching a depth of 3 km and a vertical dike below this depth. Our modeling

indicates that the horizontal extension collectively accommodated by the faults and

fissures amounts to 2.4-2.8 m, significantly higher than the amount of ~1.2 m estimated

by trilateration alone over a ~10 km baseline. The model suggests that during the 1978

event, magmatic fluids were transferred from a mid-crustal reservoir to the shallow

structures, injecting dykes and filling faults and fissures, reaching the surface in the

Ardokoba fissural eruption.