These are novel findings that are not observed for shallower earthquakes, and they provide an important clue about what causes deep earthquakes. Wiens observed that the Guttenberg-Richter relationship is different in hot, deep regions than in cold ones. This relationship is what seismologists use to measure the difference between the number of small earthquakes and the number of large earthquakes. In general, for shallow earthquakes, the answer is one. For South America and Japan, the answer is less than one-half, but for the Tonga Islands, the answer is greater than one.
Seismologists offer three major theories for the occurrence of large, deep earthquakes.
The other is ductile faulting, which occurs when kinks suddenly form in material that is too hot to be brittle. A third is related to fluids existing within the fault that aids the faulting process. Transformational faulting may predominate in very cold subduction zones, such as in the Tonga event, whereas ductile faulting may be more common in the hotter zones found in South America. But, certainly, these results indicate that temperature is vitally important in the faulting process of large, deep earthquakes in a way that is different from shallow earthquakes. Since we can't go down and see what is going on, we will need to do more analysis.