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我们怎么知道s波速度(横波)在地球的核心?这个是测量了吗?

维基百科地震波包括下面的情节S和P波速度的深度的函数。在该地区的外核的s波和横波速度显示为零但实际上它们消散,所以速度可能是复杂的。

然后在核心边界s波的速度再次显示了地球的中心,相当平近4公里/秒。

是横波的速度在地球的核心被测量还是这只是推断?如果是测量,怎么这些横波到达核心如果他们不能传播通过外核吗?

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如果波旅行只有通过* *中同时保持他们的形式(即。纵波仍保持p波和s波s波),你将获得一些有点像这个视频:https://www.youtube.com/watch?v = YctV5crEXyM。然而,波传播的标准模型是比这更复杂。打一个接口时,纵波*反射*和*折射成*其他材料。如果这发生在一个角度,它甚至会生成一个* *和*折射反映*横波(如果材料允许它!)。这样的形象:[![P-S波界面图][1]][1]你所看到的是一种纵波,朝着两个不同媒体之间的一个接口(Vp =纵波速度、横波速度,Vs = \ρ=密度)。撞击后的接口,它创造了4新浪潮!两个p波,两个s波。类似的图可以跟上一个接口。 So we can follow a hypothetical wave-path as follows: 1. There is a P-wave generated at the Earth's surface that travels down from the crust to the mantle (creating 4 new wave modes as in the figure above; **we follow the transmitted P-wave that goes down**), 2. That wavefront travels from the mantle to the outer core (which creates 3 wave modes because there is no *transmitted* S-wave! **We follow the transmitted P-wave the goes down**). 3. That wavefront travels from the outer core into the inner core (which creates 3 wave modes, because there is no *reflected* S-wave; **We follow the transmitted S-wave that goes down**). 4. The S-wave travels through the center of the Earth back up to the interface between inner core and outer core (creating 3 wave modes, because there is no transmitted S-wave; **We follow the P-wave that goes up**). 5. The P-wave travels through the outer core and hits the interface with the mantle (which creates 3 wave modes because there is no reflected S-wave; **We follow the P-wave that goes up**). 6. This P-wave further travels to the Earth's crust and surface (creating more wave-modes in the process), and is measured there. You can see some of these effects in this nice video: https://www.youtube.com/watch?v=j7eoxizmC1I that I put in the comments also. It shows P-waves in green and S-waves in red. You can see how complicated the total wavefield becomes because every interface creates new waves...so it'll be a bit hard to see the particular wavefront I described above, but you can see the general picture. [![P-wave creates S-wave in inner core][2]][2] On this snapshot you see the P-wave (in green) generating an S-wave (in red) in the inner core. So -- S-waves can exist in the inner core even when the outer core doesn't support them (because waves modes *convert*, as it's called, at interfaces), and their presence can be measured at the surface. I think that answers your question mostly. Then, of course, there is still the question of how you'd measure the speed of the S-waves in the inner core, which is rather complicated. These days, it is done by assuming some seismic model of the earth (choosing V_p, V_s, and \rho everywhere within the Earth), and modeling seismic events such as on the linked YouTube video. Then you compare real recordings against your modeled data. If there are particular misfits, you create a new model and you iterate this procedure until your model fits the recorded data 'well'. So is the shear-wave in the inner core a measured quantity or a deduced quantity? That requires a very careful definition of those terms, so I won't answer that question! Regardless, there *exists* a shear-wave velocity for the inner core that describes and explains recorded data very well. [1]: https://i.stack.imgur.com/tvgsRm.jpg [2]: https://i.stack.imgur.com/49s9f.jpg

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2020年4月4日为31

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