P‐wave tomography reveals a westward dipping low velocity zone beneath the Kenya Rift

Abstract

Three teleseismic P‐wave travel time data sets (KRISP 1985, 1989–1990; Kenya Broadband Seismic Experiment) have been inverted to obtain a new tomographic model of the upper mantle beneath the Kenya Rift. The model shows a 0.5–1.5% low velocity anomaly below the rift extending to about 150 km depth. Below ∼150 km depth, the anomaly broadens to the west toward the Tanzania Craton, suggesting a westward dip to the structure. Tomographic images to the south in Tanzania and to the north in Ethiopia also show westward dipping low velocity anomalies below depths of ∼150–200 km. The presence of westward dipping low velocity structures along much of the East African rift (Ethiopia, Kenya and Tanzania) is difficult to explain with a plume model and is consistent with some models of the African Superplume showing anomalous lower and upper mantle structure connecting at mid‐mantle depths under the western side of East Africa.

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

“…[11] A P wave tomography study of the mantle beneath Kenya by Park and Nyblade [2006] also revealed the presence of a LWA dipping to the west beneath the Tanzania Craton, consistent with earlier tomographic models from the Kenya Rift International Seismic Project (KRISP) [Green et al, 1991;Achauer and the KRISP Teleseismic Working Group, 1994;Achauer and Masson, 2002]. The limited resolution imposed by the small aperture of the Tanzania and Kenya networks, however, made it difficult for these studies to show conclusively whether the westward dipping LWA continued at depth beneath the Tanzania Craton connecting to a similar LWA under the Western branch, and also if the LWA extended through the transition zone.…”

“…[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] Park and Nyblade, 2006] and Ethiopia [Bastow et al, 2005[Bastow et al, , 2008Benoit et al, 2006].…”

“…A fast wave speed anomaly of Vp ¼ $0.6 to 1.0% is observed at depths down to 300-350 km beneath the central and northern parts of the East African Plateau comprised of the Tanzania Craton and the Uganda Basement Complex, increments from the stations. P wave arrival time delays for events recorded on collocated stations between the Kenya broadband seismic experiment (2001)(2002) and the KRISP networks (1985 and 1989-1990) are shown in Park and Nyblade [2006]. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.…”

“…But the limited vertical resolution in these models makes it difficult to determine if the LWA extends into the mantle transition zone and connects to anomalous upper mantle structure beneath eastern Africa. Regional studies of upper mantle structure in eastern Africa, on the other hand, have imaged a LWA extending from shallow depths downward into the transition zone but have not been able to ascertain if the anomaly continues through the transition zone to connect with the superplume structure in the lower mantle [e.g., Ritsema et al, 1998;Owens et al, 2000;Weeraratne et al, 2003;Park and Nyblade, 2006;Huerta et al, 2009;Adams et al, 2012].…”

Multiscale Seismic Tomography Imaging of Volcanic Complexes

“…A number of studies are dedicated to investigations of relatively small segments of the EARS using different tomographic methods (e.g. Daly et al, 2008;Jakovlev et al, 2011;Park and Nyblade, 2006;Tongue, 1992). Here I present a regional tomographic model of the upper mantle beneath the EARS constructed by Koulakov (2007) and based on global catalogues using the regional tomographic scheme shown in Figure 1.…”