M6.2 Earthquake Strikes New Zealand’s North Island: AIR
BOSTON, Jan. 20, 2014 - According to catastrophe modeling firm AIR Worldwide, at 9:52 p.m.
Eastern Time, on January 19 (3:52 p.m., local time, January 20), a magnitude 6.2 earthquake struck
New Zealand’s North Island. The epicenter was located 111 km (69 miles) northeast of Wellington,
New Zealand’s capital city and second most populous area, and 34 km (21 miles) south-southeast of
Palmerston and 37 km (23 miles) north-northeast of Masterson. Strong shaking was felt in the
vicinity of both Palmerston and Masterson. The quake struck at a depth of 28 km (17.4 miles).
According to AIR, damage to houses and their contents, power outages, rail service suspension road
closures, and a chemical spill have been reported. Nearly 30 aftershocks have been reported, most
of which were less than M4.0. Nearest the epicenter—in Palmerston North and environs as well as
Masterson where strong shaking was felt—there were reports of damage to houses and their
contents, including chimneys down and broken, windows broken, fences toppled, and items fallen
off shelves and walls.
According to AIR, the eastern margin of the Australia plate is one of the most seismically active areas
in the world due to high rates of convergence between the Australia and Pacific plates. New Zealand
lies along the 3,000 km long tectonic boundary of the Australian and Pacific plates. The epicenter of
yesterday’s earthquake is located 175 km west of the Hikuragi Trench, where the Pacific plate
subducts westward beneath the North Island. At the latitude of this event, 40.63°S, the Pacific plate
moves toward the west-southwest with respect to the Australia plate at a rate of approximately 42
mm/yr.
Microearthquake studies reveal that the subducting Pacific plate bends twice as it extends to 210 km
depth: once at a depth of 25 km and again at 70 km below New Zealand’s volcanic belt. At the bend
in the subducting plate, the load of the overlying plate is less and normal stresses build. As evidence,
small magnitude normal faulting events have been detected at depths shallower than 40 km under
the North Island. The faulting character, location, and depth of this earthquake indicate that it is an
intraplate event either within the Australia plate’s crust above the subducting Pacific plate, or within
the interior of the subducted Pacific slab, rather than a plate boundary event on the subduction zone
thrust interface.
According to AIR, New Zealand experiences fairly frequent moderate-size earthquakes. In fact, the
region within 200 km of this most recent event has experienced 35 earthquakes of M5.5 or larger
during the past century. In addition, the most event is just a few kilometers to the east of an M7.3
earthquake that struck in March 1934, and it is approximately 40 km southwest of an M6.2 and an
M6.4 earthquake near Dannekirke in March and May of 1990, respectively. The 1990 events did not
cause significant damage or fatalities.
In 2011, a 6.3-magnitude earthquake hit the city of Christchurch, in the South Island, killing 185
people.
AIR will continue to monitor this event and provide updates as warranted.