Tracing Quake’s Swath of Destruction: What Went Wrong?
KOBE, Japan (AP) _ For Yoshihiro Takeuchi, the shattered landscape hit by last Tuesday’s massive temblor is now a laboratory that contains specimens of everything he has studied.
Wooden and concrete buildings lay in piles of rubble. Others tilt at impossible angles. Elevated highways and overpasses collapsed.
Japan thought it was ready for a major quake. It wasn’t ready for this.
``The human brain has a limit, but nature doesn’t,″ said Takeuchi, chairman of the Earthquake Damage Investigation Committee for the Japan Institute of Architecture.
For Takeuchi, an engineering professor at Osaka Institute of Technology, the destruction from the magnitude 7.2 earthquake is familiar ground _ except for one phenomenon rarely spotted in his visits to quake sites in Japan and elsewhere.
``The characteristic of this quake is the middle floors of buildings collapsing,″ he told The Associated Press on Sunday during a tour of some of Kobe’s worst-hit areas. ``In past quake history, we haven’t seen this before ... except for a few isolated examples.″
The Sakura Bank building lost its fourth floor; the old city building its sixth. Part of the fifth floor of Nishishimi Hospital, in another neighborhood, collapsed.
In each case, there seemed to be little other structural damage; it was like a sandwich from which one slice of meat disappeared.
Takeuchi theorized that this quake simultaneously thrust upward and sideways, hence the wide cracks in sidewalks and the shift upward or downward of some buildings by two feet or more.
This motion also may have doomed some of the highways, which had been such a source of pride for Japanese engineers. After interstates were toppled in California quakes, they bragged that such a thing couldn’t happen here.
``All the people saying that have received a shock,″ Takeuchi said.
Japan has different construction standards for highways and buildings. The huge pillars supporting raised roads consist of concrete cores surrounded by vertical steel rods that are then wrapped with vertical steel hoops and surrounded by another coat of concrete.
In Kobe, many ruptured, the reinforcing rods snapped like matchsticks.
The horizontal-vertical movement probably was to blame, but only detailed studies will tell, Takeuchi said. He doesn’t foresee major changes to standards, but said the disaster could yield new construction techniques.
The bulk of the quake’s energy was released just below the city on what had been considered a relatively inactive fault line. It still is uncertain whether two of the Earth’s plates ground against each other, or one pushed over the other.
Although nearly 52,000 buildings were destroyed or severely damaged, Takeuchi said virtually all of those constructed since new, tighter regulations took effect in 1983 escaped largely unscathed.
A gleaming new 50-story city building, next to the damaged old one, didn’t lose a single plate from its glass facade. Another glass building next to a collapsed highway entrance ramp also came out fine.
By contrast, seemingly all of the old wooden buildings, thought to be safe from quakes because of their elasticity, collapsed into splinters.
In this quake, the side-to-side vibration was as much as 20 inches.
``For a long-wave quake like this one, the wooden structure is weak,″ Takeuchi said. ``Concrete is much safer.″
Heavy roof tiles, popular in Japan, also contributed to damage in older buildings, making them top-heavy and easily toppled.
A group of earthquake experts from 10 Japanese universities was to arrive Monday to begin a preliminary investigation.
``It is important to know how and why this (building) was damaged, but it’s also important to know why this one wasn’t,″ Takeuchi said. ``We will be looking at the designs of the buildings, their locations and other factors.″
Another aspect that will come under serious study is how to safely build on land that is situated over groundwater. In a quake, the shaking briefly creates a quicksand-like mush and buildings sink or tilt.
Much of the damage in the 1985 Mexico City quakes occurred in areas built on a dry lake bed that still contained water underneath the surface.
At Kobe, this phenomenon known as liquefaction was most evident at Port Island, reclaimed from the sea about 25 years ago. Many roads and other structures settled by two feet.
But with Japan’s shortage of space, there’s no suggestion of abandoning such land.