CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM

Abstract

Research Article| December 01, 2009 CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM S. KIM; S. KIM School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea, e-mail: srk@snu.ac.kr Search for other works by this author on: GSW Google Scholar A.A. NYBLADE; A.A. NYBLADE Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, United States of America, e-mail: andy@geosc.psu.edu Search for other works by this author on: GSW Google Scholar C-E. BAAG C-E. BAAG School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea, e-mail: baagce@snu.ac.kr Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2009) 112 (3-4): 251–260. https://doi.org/10.2113/gssajg.112.3-4.251 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S. KIM, A.A. NYBLADE, C-E. BAAG; CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM. South African Journal of Geology 2009;; 112 (3-4): 251–260. doi: https://doi.org/10.2113/gssajg.112.3-4.251 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract We investigate the thickness and seismic velocity structure of the Rukwa Rift crust by modeling seismograms from the 1994 Mw 5.9 Rukwa earthquake and teleseismic receiver functions recorded on a broadband seismic station at the southeastern end of the rift. Two methods have been used to model receiver functions, H-κ stacking and waveform inversion, yielding Moho depth estimates of 34 ± 2 km (H-κ stacking) and 38 ± 2 km (waveform inversion), and a crustal Poisson’s ratio of 0.27 ± 0.01 (H-κ stacking). A 1D average velocity model for the rifted crust has been obtained by trial-and-error modeling of the Rukwa earthquake seismograms. The best fitting velocity model obtained has a 4.5 km thick near-surface low-velocity section over a 33 km thick middle-to-lower crustal section. The velocities and thickness of the near-surface layers are consistent with the known thickness and composition of the sedimentary basin fill. The middle-to-lower crustal section is characterised by a linear velocity gradient with shear wave velocities of 3.9 km/s or higher at depths > 20 km. Crustal Poisson’s ratio in the model is 0.27. The Moho depth in the model (37.5 km) is similar to the Moho depth obtained from analysing receiver functions, suggesting that there has been little, if any, crustal thinning beneath the rift compared to the southeastern edge of the rift. The Poisson’s ratio of 0.27, in combination with the high velocities in the middle and lower crust, indicate that a significant component of the rifted crust has a mafic composition. This finding is important for understanding the occurrence of lower crustal earthquakes in east Africa, because it suggests that at least some of the crust in east Africa could be sufficiently strong at mid- and lower crustal depths to support brittle deformation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.