通过SKS分裂分析非洲中东部地区地震各向异性

SKS splitting analysis of seismic anisotropy beneath mid-eastern Africa

利用非洲台阵(Africa Array)最新的地震记录,通过测量远震SKS震相的分裂参数,详细分析了非洲中东部地区地球介质各向异性可能的成因,包括随应力场变化定向排布的裂隙和岩浆透镜体,以及橄榄石晶格的定向排布等.结果表明,现今上地幔流动导致的橄榄石晶格定向排布是其各向异性的主要成因,该结果与250km深度的地幔流动模型一致.对于少数台站出现的异常结果,则尝试用D″各向异性和双层各向异性模型来解释,并在此基础上讨论了D″各向异性的研究意义.

Mid-eastern Africa is a tectonically complex region due to the presence of Tanzania craton,several paleothrust belts and shear zones.The magmatism is active and researchers believe the existence of a mantle plume.Mechanisms and structures controlling the tectonics and geodynamics in mid-eastern Africa remain unclear and the interpretations for origins of anisotropy have not con-verged.In this paper,by taking advantage of the most recent seismic data of Africa Array,seismic anisotropy beneath mid-eastern Africa is analyzed with teleseismic SKS splitting measurements;we try to explain the sources of anisot-ropy in a variety of scenarios,such as cracks,magma-filled lenses and LPO （lattice-preferred orientation）of olivine fabrics.Fast polarization patterns at most stations are consistent with tomography based on mantle flow model at the depth of 250 km,inferring that the dominant source of anisotropy beneath this region is LPO of olivine fabrics produced by dislocation creep in the astheno-sphere.We attempt to interpret anomalous rose diagrams with D″anisotropy and double-layered anisotropy.We also discuss the significance for the research of D″anisotropy.