Sun Xinlei, Song Xiaodong, Zheng Sihua, Helmberger Don V
Department of Geology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):26-30. doi: 10.1073/pnas.0609143103. Epub 2006 Dec 20.
Compressional waves that sample the lowermost mantle west of Central America show a rapid change in travel times of up to 4 s over a sampling distance of 300 km and a change in waveforms. The differential travel times of the PKP waves (which traverse Earth's core) correlate remarkably well with predictions for S-wave tomography. Our modeling suggests a sharp transition in the lowermost mantle from a broad slow region to a broad fast region with a narrow zone of slowest anomaly next to the boundary beneath the Cocos Plate and the Caribbean Plate. The structure may be the result of ponding of ancient subducted Farallon slabs situated near the edge of a thermal and chemical upwelling.
对中美洲以西最下部地幔进行采样的压缩波显示，在300千米的采样距离内，传播时间有高达4秒的快速变化以及波形变化。穿越地核的PKP波的走时差异与S波层析成像的预测结果显著相关。我们的模型表明，最下部地幔存在一个急剧转变，从一个广阔的低速区域转变为一个广阔的高速区域，在科科斯板块和加勒比板块下方边界附近有一个最慢速异常的狭窄区域。这种结构可能是古老的法拉龙板块俯冲到热和化学物质上涌边缘附近堆积的结果。
