Herdman Symposium - Liverpool 2006
The Herdman Symposium is an annual event organised by the student geological society of the University of Liverpool. The theme this year was ‘Pushing the Boundaries… exploring the boundaries of time and space on Planet Earth’. The day consisted of five excellent lectures, at once diverse yet linked by the overarching theme, interspersed by tea coffee and a rather nice buffet lunch.
The Core-mantle boundary region – seismic observations and possible processes by Dr Tine Thomas of Liverpool University took us 2800 km down to the last few 100 km of the mantle.
Fundamentally seismic studies are based on the principle that shock waves will travel at different velocities depending on the elastic properties of what they are travelling through. Using earthquake derived shock waves, models have been developed which initially identified the three part division on the earth into crust, mantle and core. Subsequently, as data quality and analytically techniques improved, more complicated models have been developed. Seismic data available for study is mainly derived from arrays of sensors which were put out by all sides during the Cold War to detect nuclear testing by the opposition. One consequence of this is that the arrays are not necessarily positioned ideally for studies of the deep mantle. The lecture outlined that difficulty and also pointed out the current limitations in interpreting seismic waves due to the inherent properties of these waves. One big problem faced is trying to understand in two and three dimensions what the seismic data is telling you in just one. She referred to ‘tomography’ which is the technique of using waves from different positions about a 2D surface to understand what that 2D surface looks like.
A view of the core mantle boundary from www.columbia.edu/itc/ldeo/mutter/index.html