On Feb 22, New Zealand's second-largest metropolitan area, Christchurch, was struck by its second major earthquake in five months. The magnitude 6.3 temblor occurred at 12:50 p.m. local time, when many people were outside their homes.
The Christchurch quake released less than 5% of the total energy compared to the magnitude 7.3 Hanshin-Awaji quake that devastated the city of Kobe in January 1995. Yet the structural damage was horrific; as many as one-third the buildings in the city's central area may have to be demolished.
"Even for an M-6 quake occurring at a relatively shallow level of 5 kilometers beneath the Earth's surface, the scale of the damage was unexpected," Yasumichi Mifune, an authority on urban disasters, tells Weekly Playboy (March 14). "Looking carefully at videos and photos, the damage was not only confined to older edifices built of brick, such as the cathedral, but many new structures as well.
"It is certain that New Zealand, which like Japan is located in a region of frequent seismic activity, has been adopting earthquake-resistant architecture, but the disaster may have been primed by subterranean factors," says Mifune.
What Mifune means, the magazine explains, was that a previous magnitude 7.0 quake that occurred last Sept 4, with an epicenter 40 kilometers west of the city, may have caused building structures in Christchurch to weaken. Although visible damage was from the September quake was minimal, the Feb 22 "aftershock" may have served as a straw that broke the camel's back.
As professor emeritus Masaaki Kimura of Ryukyu University points out to the magazine, activity along tectonic plates tend to follow a cycle of about 30 years. The huge volcanic eruption of Mt St Helens in Washington State in 1980, for example, was followed by the magnitude 6.7 eruption along California's San Andreas fault. Likewise the 1991 eruption of Mt Pinatubo in the Philippines was followed in 2000 by seismic activity along the Marianas Trench. In 1994, movement along the Australia-Eurasia plate culminated in the catastrophic magnitude 9.3 quake off Sumatra in December 2004 and tsunami that resulted in the loss of over 200,000 lives.
What does this 30-year pattern of volcanic activity followed by a major seismic movement portend for Japan?
"Considering how the entire Pacific region maintains its balance by alternating the earthquakes and volcanic eruptions between west and east, it would suggest a strong possibility that, considering the frequency of activity off the coast of South America these past several years, Japan will be affected," Kimura remarks.
Although it's located nearly 10,000 kilometers north of New Zealand, the recent eruption of the Shinmoedake volcano in Miyazaki Prefecture may be related to activity by same Pacific Plate.
"While the Japan sector of the Pacific rim has been comparatively quiet, we should at last start anticipating the shift to more concentrated movements in the earth's crust," Kimura says.
Other signs of nearby activity on mainland Asia, such precursors of an eruption of Mt. Baekdu, on the border of North Korea and China, suggest the possibility of a shift along a major fault running through Kyushu and Honshu as far as the Chubu area, as well as increases of medium-sized quakes of magnitude 4 to 5 class in east Japan. Even a quake smaller than magnitude 7, if occurring at the relatively shallow depth of 10 to 30 kilometers beneath the surface in the greater Kanto region, could cause incalculable damage to the lives of the 30 million people living there.
Ominously, the New Zealand quakes portend increased danger for areas along the northwest section of the Pacific Plate.© Japan Today