Upper Mantle Earth Structure in Africa From Full-Wave Ambient Noise Tomography

被引:68
作者
Emry, E. L. [1 ,2 ,3 ]
Shen, Y. [2 ]
Nyblade, A. A. [1 ,4 ]
Flinders, A. [2 ,5 ]
Bao, X. [2 ]
机构
[1] Penn State Univ, Dept Geosci, University Pk, PA 16802 USA
[2] Univ Rhode Isl, Grad Sch Oceanog, Narragansett, RI 02882 USA
[3] New Mexico Inst Min & Technol, Earth & Environm Sci, Socorro, NM USA
[4] Univ Witwatersrand, Sch Geosci, Johannesburg, South Africa
[5] US Geol Survey, 345 Middlefield Rd, Menlo Pk, CA 94025 USA
关键词
Africa; rifting; craton; ambient noise; full-waveform; upper mantle; LITHOSPHERIC DISCONTINUITIES BENEATH; SEISMIC VELOCITY STRUCTURE; TRANSITION ZONE BENEATH; CONTINENTAL BREAK-UP; OKAVANGO RIFT-ZONE; EAST-AFRICAN; TRAVEL-TIME; THICK LITHOSPHERE; SPEED STRUCTURE; CAMEROON LINE;
D O I
10.1029/2018GC007804
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Our understanding of the tectonic development of the African continent and the interplay between its geological provinces is hindered by unevenly distributed seismic instrumentation. In order to better understand the continent, we used long-period ambient noise full-waveform tomography on data collected from 186 broadband seismic stations throughout Africa and surrounding regions to better image the upper mantle structure. We extracted empirical Green's functions from ambient seismic noise using a frequency-time normalization method and retrieved coherent signal at periods of 7-340 s. We simulated wave propagation through a heterogeneous Earth using a spherical finite-difference approach to obtain synthetic waveforms, measured the misfit as phase delay between the data and synthetics, calculated numerical sensitivity kernels using the scattering integral approach, and iteratively inverted for structure. The resulting images of isotropic, shear wave speed for the continent reveal segmented, low-velocity upper mantle beneath the highly magmatic northern and eastern sections of the East African Rift System (EARS). In the southern and western sections, high-velocity upper mantle dominates, and distinct, low-velocity anomalies are restricted to regions of current volcanism. At deeper depths, the southern and western EARS transition to low velocities. In addition to the EARS, several low-velocity anomalies are scattered through the shallow upper mantle beneath Angola and North Africa, and some of these low-velocity anomalies may be connected to a deeper feature. Distinct upper mantle high-velocity anomalies are imaged throughout the continent and suggest multiple cratonic roots within the Congo region and possible cratonic roots within the Sahara Metacraton.
引用
收藏
页码:120 / 147
页数:28
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