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

本研究分为两部分。一是在扎伊尔建立宽频带地震计，观测区域性地震和突发性地震。然而，这一计划因1991年9月11日发生的扎伊尔社会危机而中断。二是利用WWSSN和GDSN资料研究地幔和岩芯的非均质性。（1）核幔边界在非洲中部正下方发生了几公里的碰撞，D”层的S波速度比标准模型慢3-5%。（2）外核走时残差横向非均匀性的球谐分析表明，1度分量占主导地位（P速度的± 0.3%）。这不能用下地幔不均匀性或CMB地形来解释。我们认为，中巴绝热温度在非洲半球下相对较高，在太平洋半球下相对较低。（3）基于广泛的SmKS（m= 1，2，3）走时资料，提出了新的外核P波速度模型（KTH）。(4)S印度洋、中亚和西北太平洋D”区的流速比PREM区快1-2%。（5）研制了高精度GPS便携式地震钟。时间精度在1毫秒以内。

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.