The 6.3 earthquake
which struck New Zealand's second-largest city, Christchurch unfortunately was not entirely unexpected. The country straddles the Australian Plate to its west and the Pacific Plate, on its eastern side. And that makes for an active volcano and fault system when these plates collide.
And collide they do. Researchers say that New Zealand is home to about 14,000 earthquakes a year. Most hardly register but approximately 20 reach a top magnitude of 5.0.
Instead of moving smoothly past each other, the plates also move toward each other, resulting in a succession of "small rapid motions," accompanied by at least one earthquakes.
In fact, the Alpine Fault, which runs for about 600 kilometers through the South Island, suffered major eruptions in 1717, 1620, 1450, and 1100. ("Major" defined as an earthquake with an estimated magnitude of 8.0.)