3 ms·
As for what the east-west axis means... According to the paper, they use a cylindrical anisotropy model and the best-fit axis is located at (9° N, 89° W) or its
by kens 12y ago
As for what the east-west axis means... According to the paper, they use a cylindrical anisotropy model and the best-fit axis is located at (9° N, 89° W) or its antipode at (9° S, 91° E). In other words, the crystals point along an axis near the equatorial plane through Central America and Southeast Asia.
The paper is pretty vague about why this would occur: "may represent a tectonic evolution of the inner core and thus our finding may indeed offer ‘clues about the inner-core history: its age, thermal process, and possibly an early convective event’."
Paper is available at http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2354.html http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo23...
- tjradcliffe 12y agoBut the core doesn't rotate at the same rate as the crust: http://news.harvard.edu/gazette/1996/08.15/PuttingaNewSpin.html http://news.harvard.edu/gazette/1996/08.15/PuttingaNewSpin.h... (or has this been proven wrong?)
- kens 12y agoThat's very interesting. If the inner core rotates 3 degrees a year and the earthquake data covers 20 years, that would be a 60 degree shift from start to end of the data set. I looked over the paper again, and they don't mention this at all. Edit: I emailed the author of the paper (Xiaodong Song). He says that more recent work suggests 0.3-0.5 deg/year for core rotation. (This would make the rotation much less important.) http://www.geology.illinois.edu/people/xsong/Sites/papers/zhangetal05_science.pdf http://www.geology.illinois.edu/people/xsong/Sites/papers/zh... http://www.geology.illinois.edu/people/xsong/Sites/papers/lindner_etal10_jgr.pdf http://www.geology.illinois.edu/people/xsong/Sites/papers/li...