Location of today's earthquake in New Zealand from this site. Note that the earthquake was on the South Island, whereas Wellington is on the southwestern tip of the North Island. |
Tectonic setting of New Zealand from Wiki here |
New Zealand has a wide variety of active geologic phenomena--earthquakes, volcanic eruptions, geothermal areas, and landslides--because it sits at the boundary of the Australian and Pacific Plates. In the north (see graphic) the Pacific Plate is subducted under the Australian Plate, but in the south, the reverse happens: the Australian Plate is subducted under the Pacific Plate. These two subduction zones are connected by the Alpine Fault that runs along much of the west coast of the south island of New Zealand. Subduction rates are high--tens of millimeters per year, but so are erosion rates. The mountains rise about 10 mm/year, but are eroded down at about the same rate. The combination produces some of the most beautiful mountains in the world on the south island. The Alpine Fault is considered to be at high risk of producing a major earthquake in the next 40 years (see GNS).
Recent activity has been in the vicinity of the Marlborough fault system and, in particular, the M7.1 Canterbury (2010) and Christchurch (2011) earthquakes were on relatively minor faults. The fault system was named after the 1848 M7.5 earthquake centered in the Marlborough district of the South Island, a quake that produced substantial damage in the Wellington area as well. The European population of Wellington was approximately 4500 at the time; only 3 people died. Because stone and brick buildings suffered much more severe damage than wooden ones, for a time many buildings in the area were constructed of wood. But, after only 25-30 years, the institutional memory was lost and stone and brick buildings returned, partially encouraged by concerns about fire. At the beginning of the 20th century the country seemed calm, and the New Zealand Official Yearbook included the comment: "earthquakes in New Zealand are rather a matter of scientific interest than a subject for alarm." Quote from this source. The population of Wellington in 2012 was 385,600.