Seismic tomography scans have huge potential in the geography classroom. But what are they? In simple terms, they are like a CAT scan of the interior of the Earth. They are created by measuring the speed of seismic waves. Areas, where there is a low velocity, correspond with hotter, less dense zones in the mantle (e.g. a mantle plume). To find out more about seismic tomography scans take a look at this excellent guide by Earth Scope.
There are a number of tools available to generate seismic tomography scans. Our favourite is the Hades Underworld Explorer. The interface is made to facilitate the discovery and visualisation of mantle anomalies. A tomographic model can be generated by either selecting a section preset or by dragging markers to generate a cross-section of the mantle.
In the example below, a selection has been made in the northwest Pacific, in Asia.
A selection in the north-west Pacific
The website then generates a tomography scan showing the cross-section of the mantle.
The subduction of the Eurasian plate by the Pacific Plate
The depth of the mantle is shown in kilometres on the x-axis. The key shows velocity anomalies. In the case of the tomography scan above the colder, more dense material is shown in blue, while the hotter, less dense material is shown in red. Based on this we can see the destructive margin formed by the Eurasian plate being subducted by the Pacific plate. The Pacific Plate sinking into the mantle as illustrated by the cooler crust (shaded blue), reaches a depth of around 800 km.
In the example below the mantle plume at Hawaii is clearly visible (accessed via the drop-down menu).
Hawaii mantle plume
Tomography scans lack the resolution required to image plumes deep within the mantle.
The tomography scan below illustrates the Rift Valley in eastern Africa.
Rift valley transect
Rift valley tomography scan
The tomography scan below shows the Northern Atlantic.
North Atlantic Transect
North Atlantic Tomography scan
In the tomography scan above we can see that the conduit spreads laterally across the North Atlantic, to a depth of around 900 km. There is a conduit feeding this between 900-1200 km along the transect at a depth of around 1000 – 1500 km.
Note: The settings in the Hades Underworld Explorer allow you to customise your tomography scan.
Tomography Scan Settings
Alistair Hamill has shared a number of resources on the use of seismic tomography on Twitter and inspired our interest in this area. Below are a selection of tweets by Alistair that are well worth exploring.
Take a look at Alistair’s timeline on Twitter to see how he has used them in his classroom.
If you know of resources to support the use of seismic tomography scans please share them in the comments below.