East African Rift

Geodetic Monitoring of the 2005 Da'Ure rifting event, Afar (Ethiopia)

Collaboration R. Buck (Lamont-Doherty Observatory), T. Wright (Oxford University, UK),
C. Ebinger (Royal Holloway University, UK), E. Lewi and L. Asfaw (University of Addis Ababa, Geophysical Observatory)

Technical support from UNAVCO

A nascent seafloor spreading center in the Afar depression, Ethiopia, has experienced increased seismicity and a explosive fissural volcanic eruption between September 14 and ~October 8, 2006. Early InSAR results show that these events have been accompanied by the intrusion of a ~60 km long dike with up to 8 m of opening. Scientists from Purdue University and Lamont-Doherty Observatory in the U.S., Oxford University and Royal Holloway University in the U.K., and the University of Addis Ababa in Ethiopia have installed 10 continuous GPS stations to better understand this major diking event, the largest to have occurred on land in the era of satellite geodesy. Technical support was essential and provided by UNAVCO.
Part of the field crew, including E. Calais (Purdue), R. Buck (Lamont) J. Elliot (Oxford), Negassa and Worku (Ethiopian Mapping Agency), the local vice-chairman Ismael, one Afari policeman, and our 3 Afari camel drivers.

Tectonic map of the northern part of the Main Ethiopian Rift and Afar (from Hayward and Ebinger, 1996). Black dots around the DaUre (=Boina) segment are seismic events that accompanied the 2005 dike intrusion (NEIC catalog). Thin dashed lines show ESA radar frames. The northern Afar depression is a piece of recent ocean floor characterized by 60~km-long axial volcanic ranges with aligned chains of basaltic cones, fissural flows, punctuated by rhyolitic volcanoes. These "magmatic segments" are similar in size, morphology, and spacing to those observed at slow-spreading mid-oceanic ridges. The 2005 Da'Ure diking event ruptured the entire length of a previously mapped magmatic segment. It is comparable in magnitude to the 1975-1984 series of dike intrusion in the Krafla area, Iceland, but seismic data suggest that most of the Da'Ure dike intrusion occurred ins less than 6 days. Simple elastic modeling based on an inversion of InSAR data shows that the Da'Ure segment opened by up to 8 m between depths of 2 and 8 km, corresponding to a total intrusion volume of ~2.5 km^3. Approximately 20% of the magma was sourced from shallow chambers beneath two stratovolcanoes at the northern end of the segment.

Dike intrusions account for most of the separation of plates at divergent boundaries. The Krafla dike intrusion episode in Iceland, where a sequence of ~10 dike intrusions produced as much as 9 m widening of the ~100 km-long rift zone between 1975 and 1979, has been instrumental to our understanding of diking and spreading processes. However, geodetic measurements did not capture the syn- and post-dike deformation with the spatial coverage and precision possible today. The 2005 Da'Ure event, comparable in length and magma volume with the Krafla episode in Iceland, offers an unprecedented opportunity to directly observe and quantify diking and post-diking processes, ubiquitous but not directly accessible at oceanic spreading centers.
Continuous GPS station DA03, located about 3 km from the rift axis. A Trimble Zephyr antenna is mounted on a 0.5 m metal pole anchored in bedrock. GPS receiver is a Trimble NetRS. Power is provide by solar panels.

A nascent seafloor spreading center in the Afar depression, Ethiopia, has experienced increased seismicity and a explosive fissural volcanic eruption between September 14 and ~October 8, 2006. Early InSAR results show that these events have been accompanied by the intrusion of a ~60 km long dike with up to 8 m of opening. Scientists from Purdue University and Lamont-Doherty Observatory in the U.S., Oxford University and Royal Holloway University in the U.K., and the University of Addis Ababa in Ethiopia have installed 10 continuous GPS stations to better understand this major diking event, the largest to have occurred on land in the era of satellite geodesy. Technical support was essential and provided by UNAVCO.	Part of the field crew, including E. Calais (Purdue), R. Buck (Lamont) J. Elliot (Oxford), Negassa and Worku (Ethiopian Mapping Agency), the local vice-chairman Ismael, one Afari policeman, and our 3 Afari camel drivers.
Tectonic map of the northern part of the Main Ethiopian Rift and Afar (from Hayward and Ebinger, 1996). Black dots around the DaUre (=Boina) segment are seismic events that accompanied the 2005 dike intrusion (NEIC catalog). Thin dashed lines show ESA radar frames.	The northern Afar depression is a piece of recent ocean floor characterized by 60~km-long axial volcanic ranges with aligned chains of basaltic cones, fissural flows, punctuated by rhyolitic volcanoes. These "magmatic segments" are similar in size, morphology, and spacing to those observed at slow-spreading mid-oceanic ridges. The 2005 Da'Ure diking event ruptured the entire length of a previously mapped magmatic segment. It is comparable in magnitude to the 1975-1984 series of dike intrusion in the Krafla area, Iceland, but seismic data suggest that most of the Da'Ure dike intrusion occurred ins less than 6 days. Simple elastic modeling based on an inversion of InSAR data shows that the Da'Ure segment opened by up to 8 m between depths of 2 and 8 km, corresponding to a total intrusion volume of ~2.5 km^3. Approximately 20% of the magma was sourced from shallow chambers beneath two stratovolcanoes at the northern end of the segment.
Dike intrusions account for most of the separation of plates at divergent boundaries. The Krafla dike intrusion episode in Iceland, where a sequence of ~10 dike intrusions produced as much as 9 m widening of the ~100 km-long rift zone between 1975 and 1979, has been instrumental to our understanding of diking and spreading processes. However, geodetic measurements did not capture the syn- and post-dike deformation with the spatial coverage and precision possible today. The 2005 Da'Ure event, comparable in length and magma volume with the Krafla episode in Iceland, offers an unprecedented opportunity to directly observe and quantify diking and post-diking processes, ubiquitous but not directly accessible at oceanic spreading centers.	Continuous GPS station DA03, located about 3 km from the rift axis. A Trimble Zephyr antenna is mounted on a 0.5 m metal pole anchored in bedrock. GPS receiver is a Trimble NetRS. Power is provide by solar panels.