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Seismic Activity and the Lithosphere

Earth's structure

Q: What sort of seismic activity was seen on earth prior to the period in which the continental lithosphere achieved widespread tectonic stability and craton stabilization took place, would there have been far more earthquakes prior to this stabilization?

From Saman Vjestica (April 2011)

Reply by Dr Ted Nield

It is very difficult to see back as far in time as would be necessary to take us to a moment before the current configuration of lithosphere, mantle and core was established. Rocks from that time (and we are talking here about rocks probably older than 3500 million years) do not survive in great numbers and are extremely hard to interpret. Even answering a basic question as to the nature of the early crust and its thickness, is tough. One might expect there to have been a thinner crust with higher heatflow; but that is not necessarily so.

Speaking about area, there is some suggestion that over time lithospheric plates have grown bigger. It may well be that at the time that the Greenstone Belts of southern Africa were created, the crust was divided into many smaller cratonic proto-continents separated by relatively very much wider mobile belts. This is likely to have meant greater crustal plasticity, which may in turn have meant more frequent seismic activity at surface – but whether this would have meant more large magnitude earthquakes is conjectural. The maxima for seismic events (somewhere over M9) that currently apply are dependent upon rock strength. And on a hotter, plastic Earth, such strength may not have been achieved and hence stress would have been released more easily or would have been accommodated in ductile rather than brittle behaviour.