SEISMIC ANISOTROPY IN THE MANTLE BENEATH AN OCEANIC SPREADING CENTER

被引:29
作者
BLACKMAN, DK [1 ]
ORCUTT, JA [1 ]
FORSYTH, DW [1 ]
KENDALL, JM [1 ]
机构
[1] BROWN UNIV, DEPT GEOL SCI, PROVIDENCE, RI 02912 USA
关键词
D O I
10.1038/366675a0
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
BENEATH an active mid-ocean ridge, the mantle upwells in response to the divergence of the newly formed plates, leading to high temperatures and pressure-release melting below the ridge axis. The width of the upwelling region and the amount of melting depend on mantle rheology1-5, but all models predict a maximum decrease in seismic velocity at the ridge axis. It has also been suggested, however, that the alignment of anisotropic minerals by shear in the upwelling mantle will increase seismic velocity for rays travelling subvertically through the upwelling zone6,7. Here we report the observation of a consistent pattern of anomalously early P-wave arrival times at an array of ocean-bottom seismographs deployed across the axis of the southern Mid-Atlantic Ridge: P-waves from distant earthquakes arrive earlier at stations near the axis than at those further away. Our results are consistent with a model of anisotropy in which the degree of mineral alignment is greatest directly beneath the ridge axis, and significant anisotropy extends tens of kilometres from the axis.
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页码:675 / 677
页数:3
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