The article is misleading. It's not like there is a free body of water in the lower mantle.
The water is carried there in hydrous minerals that dehydrate as they become unstable at
the increased pressure/temperature of the lower mantle. That water, which was originally near the earth's surface, is then absorbed as new and different hydrous minerals form, ones that are stable in the lower mantle--like Mg-perovskite. One of interesting results of this research is the notion
of water recycling on a whole earth scale, not just the upper few km.
Most modern seismometers have low frequency corners below 0.01 Hz. This hum signal is not
so tricky to detect--it shows up everywhere. The tricky part is figuring out what causes it.
Slashdot Mirror
The article is misleading. It's not like there is a free body of water in the lower mantle. The water is carried there in hydrous minerals that dehydrate as they become unstable at the increased pressure/temperature of the lower mantle. That water, which was originally near the earth's surface, is then absorbed as new and different hydrous minerals form, ones that are stable in the lower mantle--like Mg-perovskite. One of interesting results of this research is the notion of water recycling on a whole earth scale, not just the upper few km.
Most modern seismometers have low frequency corners below 0.01 Hz. This hum signal is not so tricky to detect--it shows up everywhere. The tricky part is figuring out what causes it.