The role of fluids in lower-crustal earthquakes near continental rifts

Earthquake generation Earthquakes in the lower continental crust of the Earth are rare, as the lower crust is thought to be too hot to allow brittle failure. So it is surprising that they occasionally occur where continental crust is rifting apart. A study of three-dimensional crustal structure and seismicity in the Taupo Volcanic Zone, an active continental rift in New Zealand, has now provided insight into how these earthquakes arise. The crustal earthquakes form a continuous band along the rift, and often occur in swarms, suggesting fluid movement in critically loaded fault zones. Seismic velocities within the band are consistent with the presence of fluids, and the linking of upper- and lower-crust seismicity to crustal structure point to a common explanation for all of the seismicity — probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids.