Broad-band Seismological Observation in the African Continent and Study of the Earth's Deep Interior

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This study was divided into two parts. The one is to set-up the broad-band seismometer in Zaire and to observe the regional and teleseismic events. However, this program was interrupted by the social crisis in Zaire that occurred on September 11, 1991. The other is to study the heterogeneity in the mantle and core by using the data of the WWSSN and GDSN. The followings are the brief summary of the present study: (1)The core-mantle boundary (CMB) was bumped several kilometers just beneath the central Africa and the S velocity in the D" layer was 3-5% slower beneath Africa than the standard model. (2)Spherical harmonic analysis of the lateral heterogeneity of the travel time residuals in the outer core indicated that degree 1 component was most dominant (+/-0.3% of P velocity). This could not be explained by lower mantle heterogeneity nor CMB topography. We suggested that adiabatic temperature at CMB were relatively higher beneath the African hemisphere and lower beneath the Pacific hemisphere. (3)Based on the extensive data set of travel times of SmKS (m=1,2,3), new P velocity model (KTH) of the outer core was presented. (4)S velocity in the D" region beneath the Indian Ocean, Central Asia and N.W. Pacific Ocean were 1-2% faster than those of PREM. (5)GPS portable clock with high precision was developed for the field seismometry. The time accuracy was within 1 milli-seconds.