HR: 09:30h
AN: T31F-07    [Abstracts]
TI: Seismological Investigation of Rift Related Uplift: The Rwenzori Network in Western Uganda
AU: * Rümpker, G
EM: rumpker@geophysik.uni-frankfurt.de
AF: Institute of Geosciences, University of Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany
AU: Jakovlev, A
EM: jakovlev@geophysik.uni-frankfurt.de
AF: Institute of Geosciences, University of Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany
AU: Batte, A
EM: abatte@sci.mak.ac.ug
AF: Geology Department, Makerere University, P.O. Box, Kampala, 7062, Uganda
AU: Lindenfeld, M
EM: mirzar@geophysik.uni-frankfurt.de
AF: Institute of Geosciences, University of Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany
AU: Schumann, A
EM: geo-andy@gmx.de
AF: Geology Department, Makerere University, P.O. Box, Kampala, 7062, Uganda
AU: Woelbern, I
EM: woelbern@geophysik.uni-frankfurt.de
AF: Institute of Geosciences, University of Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany
AB: We present first results from a temporary seismic network located within the western branch of the East-African rift system. The project aims to constrain the development and uplift of the Rwenzori mountain range and its relation to the formation of the rift zone. Local and teleseismic earthquake recordings are used to image structures of the crust and upper mantle within the region. A temporary network consisting of 23 mobile broadband and short-period seismic sensors was operating during a period of about 16 months until October 2007. The stations were located mainly along two profiles in the westernmost part of Uganda near the Congo border. One profile was situated within the rift along the eastern flank of the Rwenzori Mountains, approximately between 0.2°S and 0.9°N. The second profile was located nearly perpendicular to the rift, extending from the eastern rift shoulder into the rift valley and further crossing the northern part of the Rwenzori Mountains. Additional seismic stations were placed on the rift shoulder in the South-East and the North-West to improve the localization of events. A number of seismological methods are used to study crustal and upper-mantle structure. The localization of sources and fault-plane solutions provide information on active fault zones and on current tectonic movements. Local and teleseismic tomography are applied to determine the 3D velocity structure in the area under investigation and to detect velocity anomalies in the crust and the upper mantle down to approximately 300 km depth. Moho depths are derived from converted phases using receiver functions. Furthermore, shear wave splitting is analyzed to detect regions of anisotropy and their relation to deformation processes and mantle flow. The first analysis of the data shows high seismic activity of the Rwenzori region. Approximately 500 events per month have been located. Focal depths are concentrated between 10 and 20 km. Local P and S-wave tomography using data of the first few months shows significant low velocity anomalies in the northern part of the network, correlated with active volcanic fields and hot springs. From receiver functions, crustal thicknesses of about 23 km have been found beneath the eastern flank of the rift. The interpretation of our results will provide constraints for the modeling of geodynamic processes responsible for the formation of the Rwenzori Mountains.
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting