The theory of plate tectonics states that Earth’s surface is made up of several internally rigid plates that coherently translate across the underlying mantle, pulling apart to build new ocean basins and crashing into one another to form mountain belts and subduction zones. Given their key underlying role in modulating geological processes that occur on the surface, it comes as no surprise that geologists are very interested in understanding the properties of these tectonic plates. How thick are they? Does this thickness vary as a function of space and time? How hot is the underlying mantle? And what is its viscosity (or stickiness), which inherently controls rates of plate motion?
One of the most successful and widely used techniques to image the upper mantle is seismic tomography. Acoustic energy generated during earthquakes travels through the Earth to seismometers, and using the locations and travel times of this energy allows us to build 3D maps of the variation in seismic velocity within the interior. Seismic velocity on it’s own is not the most interesting parameter, but because it is known to vary as a function of temperature, composition, and grain size, we can use it to build maps of plate thickness and mantle temperature structure.
In this study, we generate these maps by combining some of the latest seismic tomography models with recent laboratory experiments on the deformation of mantle rocks at seismic frequencies. Our results can be used to delineate variations in plate thickness, estimate the present-day mantle temperature beneath the source regions of volcanic rocks, and predict mantle viscosity structure for use in convection studies and sea-level modelling. We finish by using our refined picture of upper mantle density anomalies to predict the pattern of present-day dynamic topography, and obtain the best fits to independent observations in the oceanic realm of any global mantle convection simulation to date.