Magnitude 6.2 Quake Strikes New Zealand’s North Island: AIR Analysis

January 21, 2014

Catastrophe modeling firm AIR Worldwide, reported: “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.”

AIR explained that 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 [1860 miles] long tectonic boundary of the Australian and Pacific plates.

“The epicenter of yesterday’s earthquake is located 175 km [108.5 miles] 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.

“Micro earthquake 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 [124 miles] of this most recent event has experienced 35 earthquakes of M5.5 or larger during the past century. In addition, the 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.

Source: AIR Worldwide

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