Crustal thickness estimate at AAE (Addis-Ababa, Ethiopia) and NAI (Nairobi, Kenya) using teleseismic P-wave conversions


Long-period teleseismic P waves recorded at AAE (Addis Ababa, Ethiopia) and NAI (Nairobi, Kenya) show comparable Ps conversions on the radial component of ground motion. The timing and amplitude of the Ps conversions are modeled with synthetic seismograms to get an estimate of crustal thickness under both stations. Instrument response and effective source time function are removed from the data using a P-wave equalization procedure. The timing of the Ps conversions, relative to direct P, suggests that both stations have similar crustal thickness. Using constraints on crustal velocities determined by previous surface wave dispersion and travel-time studies, the Ps-P timing suggests a crust of 41 km thickness. This agrees reasonably well with previous crustal estimates. Tangential wave forms exhibit large amplitudes and are consistent at most backazimuths. However, these wave forms could not be explained with models containing simple planar dipping interfaces. The crustal thickness of 41 km taken in conjunction with the close proximity of the stations to the rift zone suggests that crustal thinning is localized to the rift itself. © 1985.

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