HR: 0830h
AN: S51C-0063 [PDF]
TI: Tomographic Imaging of the Northern Ethiopian Rift - a Transition From Continental to Oceanic
Rifting
AU: * Bastow, I
EM: ibastow@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT
United Kingdom
AU: Stuart, G
EM: graham@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT
United Kingdom
AU: Kendall, J
EM: m.kendall@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT
United Kingdom
AU: Ebinger, C
EM: c.ebinger@gl.rhul.ac.uk
AF: Royal Holloway University of London, Royal Holloway University of London, Egham, TW20 OEX
United Kingdom
AU: Ayele, A
EM: atawon@yahoo.co.uk
AF: Geophysical Observatory, University of Addis Ababa, Addis Ababa, PO 1176
Ethiopia
AB:
The EAGLE broadband array consisted of 30 sensors distributed over an 250 km
x 250 km area of the northern Ethiopian Rift in order to study the crust and
upper mantle structure of a region of transition from continental to oceanic
rifting.
Analyses of teleseismic relative residual travel times indicate a variation of the order of 1 sec; slower arrivals to the NW
of the Rift on the uplifted Ethiopian Plateau and faster arrivals to the SE towards the Somali plate.
Tomographic inversion of 3614 P-wave and 800 S-wave relative arrival times using the method of VanDecar images a narrow
$\sim$70 km wide low velocity upwelling (1.5% P-wave velocity anomaly), well resolved to 300 km beneath the Rift in the
southern part of the array. This anomaly broadens with depth northwards into Afar as asthenospheric (oceanic) rifting
processes begin to take over from the lithospheric (continental) ones prevalent in the south. An off-rift axis E-W low
velocity anomaly just south of Addis Ababa corresponds to the surface manifestation of a line of Quarternary volcanoes.
Interestingly the maximum upper mantle low velocity anomaly is offset by about 25 km to the NW from the location of rift
magmatic segments. S-wave anomalies show a similar rift structure to the P-wave results but are of twice the magnitude.
DE: 7218 Lithosphere and upper mantle
DE: 8109 Continental tectonics--extensional (0905)
DE: 8180 Tomography
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting