Seismo-volcanic crisis in Afar: the 2005 Boina rupture-eruption sequence

Abstract
Continental rupture models emphasize the role of faults in extensional strain accommodation; extension by dike intrusion is commonly overlooked. A major rifting episode that began in September, 2005 in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array, direct observation of fault patterns, and geodetic data document ongoing strain and continued dike intrusion along the ~60 km-long Dabbahu-Wal’is rift segment. Epicentral locations lie along a ~3 km-wide, ~50 km-long swath that curves into the SE flank of Dabbahu volcano; a second strand continues to the north toward Gab’ho volcano. Two additional dike intrusions in June and July, 2006 indicate a central feeding source for basaltic magmas (Keir et al., 2009; Hamling et al., 2009). We interpret the depth distribution of microseismicity as the dike intrusion zone; the dikes rise from ~10 km to the near-surface along the ~60 km-long length of the tectono-magmatic segment. Focal mechanisms indicate slip along NNW-striking normal faults, perpendicular to the Arabia-Nubia plate opening vector. The seismicity, InSAR, continuous GPS, and structural patterns all suggest that magma injection from lower or sub-crustal magma reservoirs continued at least 3 months after the main episode. Cote et al (submitted) measure the low frequency content of volcano-tectonic earthquakes recorded on a temporary broadband seismic array following the September 2005 dike intrusion and volcanic eruption sequence in the Afar rift, Ethiopia. Stations at all 9 sites show signals with long low frequency codas. Strong variations in signal amplitude, frequency content and coda length are seen even between stations separated by only 2 km. The patterns of seismicity after the 2005 dike intrusion provide a 3D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment.
Full Report
Selected external publications resulting from this GEF loan
- Cote, D.M., Belachew, M., Quillen, A.C., Ebinger, C.J., Keir, D., Ayele, A. and Wright, T., 2010, Low frequency hybrid earthquakes near a magma chamber in Afar: quantifying path effects, Bulletin of the Seismological Society of America, 100, pp1892-1903, doi: 10.1785/0120090111
- Ebinger, C., Ayele, A., Keir, D., Rowland, J., Yirgu, G., Wright, T., Belachew, M. and Hamling, I., 2010, Length and timescales of rift faulting and magma intrusion: the Afar rifting cycle from 2005 to present, Annual Review of Earth and Planetary Sciences, 38, pp437-464, doi: 10.1146/annurev-earth-040809-152333
- Hammond, J.O.S., 2014, Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: The anisotropic H-κ stacking technique, Geochemistry, Geophysics, Geosystems, 15(4), pp1316-1332, doi: 10.1002/2013GC005186
