GNS Science geophysicist Dr Grant Caldwell and colleagues have reported that water deep beneath earthquake zones in New Zealand triggers tremors. Caldwell and his colleagues were able to determine how water is moving and concentrating below fault zones in the northern part of the south island, where the Pacific plate slides underneath the Australian plate. The team used magnetotellurics, which probes earthquake zones using naturally occurring low frequency electromagnetic waves generated by solar activity and lightning storms, to obtain a picture of what was happening down to 100 kilometres below the earth’s surface. Caldwell says scientists believe pressure of water building up beneath the fault can get so great it can cause it to rupture, leading to an earthquake. “The addition of water into the base of the fault makes it easier for the fault to fail,” he said. The study is published in the prestigious journal Nature.