The 2015 earthquake swarm in the Fentale volcanic complex (FVC): A geohazard risk for Ethiopia's commercial route to the Djibouti port.

Abstract

We investigate rare seismicity in the neighborhood of the Fentale volcano, main Ethiopian rift that occurred in spring 2015 using data recorded by the Ethiopian Seismic Station Network. Over 1350 earthquakes are located and a seismic swarm is observed to the northeast of Fentale volcano, with the largest earthquake having a magnitude of 4.3 ML. Several VT (volcano-tectonic) and LP (long-period) events are observed in the swarm, indicating that it is induced by magmatic intrusion, consistent with dike-induced deformation in the same area inferred from satellite geodesy. The seismic activity commenced at about 40 km depth and migrated southwestward as it shallowed, towards Fentale volcano, suggesting that the dike feeding system might be influenced by the magma rich Afar Depression further to the northeast rather than the adjacent Fentale volcano. An earlier cluster of seismicity in the same area was recorded by a temporary deployment of seismic stations that ran from November 2001 to January 2003; extensive clusters of less well recorded seismic activity in the region occurred in June 1989, January–February 1981, October–November 2003, and 2004. Such frequent seismicity at the Fentale Volcanic Complex coupled with the adjacent fast-growing Lake Basaka poses an eminent and significant risk to Ethiopia's access to Djibouti port, its most important commercial route. This should be a wakeup call to concerned stakeholders to take precautionary measures by developing risk management and rapid response strategies.