We see sheer waves travelling through it, and therefore we know that it must be solid. That's how we know that the mantle is solid. But there are other layers within the earth, if you go even deeper, ther are liquid,. And we don't get sheer wayoes travelling through those. You can actually do quite a nice little experiment to show this yourself. For example, if you take a hard boiled egg and a raw egg and spin them on, put them on a table, down on atable, and then spin them. So what you 're doing by spinning them is your putting a sheer stress or sheerfo on to the egg. Now the hard boiled egg will keep
Melvyn Bragg and guests discuss the study of earthquakes. A massive earthquake in 1755 devastated Lisbon, and this disaster helped inspire a new science of seismology which intensified after San Francisco in 1906 and advanced even further with the need to monitor nuclear tests around the world from 1945 onwards. While we now know so much more about what lies beneath the surface of the Earth, and how rocks move and crack, it remains impossible to predict when earthquakes will happen. Thanks to seismology, though, we have a clearer idea of where earthquakes will happen and how to make some of them less hazardous to lives and homes.
With
Rebecca Bell
Senior lecturer in Geology and Geophysics at Imperial College London
Zoe Mildon
Lecturer in Earth Sciences and Future Leaders Fellow at the University of Plymouth
And
James Hammond
Reader in Geophysics at Birkbeck, University of London
Producer: Simon Tillotson