Transient rift opening in response to multiple dike injections at Manda Hararo (Afar, Ethiopia) imaged by a new method for high-rate InSAR time-series

Raphaël Grandin⁽¹⁾, Anne Socquet⁽¹⁾, Marie-Pierre Doin⁽²⁾, Eric Jacques⁽¹⁾, Jean-Bernard de Chabalier⁽¹⁾ and Geoffrey King⁽¹⁾

⁽¹⁾ Institut de Physique du Globe de Paris, 4, place Jussieu, 75252 Paris Cedex 05, France
⁽²⁾ Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France

Abstract

ENVISAT InSAR data spanning the time intervals separating twelve dike intrusions at Manda Hararo-Dabbahu rift (Afar, Ethiopia) from 2005 to 2009 shows that deformation occurs in the inter-diking period. These transient deformations can be explained by the presence of six sources that can be interpreted as inflating or deflating magma chambers. These deformational patterns are first tracked in the interferograms by a simple cross-correlation method. In a second step, time resolution is increased by combining the data acquired on four different InSAR tracks, through time-dependent elastic models.

The sustained deflation of a deep magma chamber at Dabbahu in the six months following the main rifting event of 2005, slow decelarating post-eruptive re-inflation of two shallow magma reservoirs below Dabbahu and Gabho volcanoes, and a deflation signal of deep origin on a neighbouring rift segment are clearly imaged.

In contrast, rapidly changing deformations are observed at the centre of the Manda Hararo rift segment. For the first time, transient deformations are monitored in the weeks/months following the diking events, with pulses of activity after the dike intrusions, followed by an exponential-like decay. This signal may be associated with the recharge of the central magma reservoir involved in feeding the 2005-2009 dikes. Alternately, the predominantly horizontal mode of deformation suggests a short-term interaction between the visco-elastic response of the crust to tectonic forcing, and the process of hydraulic connectivity within the central magma plumbing system.