SCIENCE-EGYPT: Earthquake Fear Brings Tremors

By Cam McGrath Reprint | | Print |

Cam McGrath

CAIRO, Oct 17 2002 (IPS) - The tremors that rocked Cairo in August have left the city fearing for its future if another earthquake were to hit.

Tremors measuring 4.7 on the Richter scale rattled the city on August 24, damaging close to 50 buildings and sending terrified residents into the streets. It reminded residents of the earthquake that hit Cairo on October 12, 1992 that left 540 dead and more than 10,000 injured. And it reminded residents that lessons have not been learned. Faulty construction places about a million residents at risk.

Umm Mohammed (39) remembers the earthquake ten years ago like it was yesterday. The walls of her apartment began to crumble. She grabbed her two young sons but could not run on the violently shaking floor. She took cover beneath a table until the tremors stopped. "We thought the building was going to collapse," she says.

Many buildings did collapse, causing most of the casualties. It was a moderate earthquake measuring 5.8 on the Richter scale with its epicentre in Dashur, 35 kilometres southwest of Cairo. The earthquake lasted less than a minute but the damage it caused was enormous.

Low-income apartment buildings in Cairo are built usually with a concrete frame and brick walls – a recipe for disaster. "Concrete is very brittle," says Medhat Haroun, professor of construction engineering at the American University in Cairo. "What you want in an earthquake are materials which can take the horizontal motion and return to their original state. Bricks absorb some of the shock, but they have little resistance. A brick building can immediately disintegrate and kill everyone inside."

Earthquakes under 6.0 in magnitude rarely cause extensive damage. But in Egypt a relatively small tremor can send dozens of buildings crashing to the ground. The large clay and sand content in soil amplifies ground motion, but more significantly, shoddy construction is to blame.

"The main reason for the extensive damage (in 1992) was that buildings did not follow building codes and were poorly maintained," says Sherif Mourad, professor of structural engineering at Cairo University. More than 5,000 buildings collapsed in the 1992 earthquake, and more than 11,000 – including dozens of historic monuments – were severely damaged. Estimates of material damage start at 1.2 billion dollars.

Thousands of families were left homeless. Some, like Umm Mohammed, still live in makeshift housing awaiting new homes promised by the government. Others have moved into illegally constructed additions over the roofs of low buildings. These are certain to crumble if another quake hits.

There is serious risk of that happening, says Aboul Ela Mohammed, deputy director of the National Seismological Lab Network (NSLN). Established in 1994, the NSLN is a network of 50 monitoring stations to monitor seismic activity and map earthquake risk. "Our main purpose is to mitigate earthquake damage," says Mohammed. The network is also geared to help with emergency response and to determine the choice of construction materials and insurance rates.

The centre cannot predict when a big earthquake may hit, but seismic activity often precedes a large earthquake by weeks or months. The 1992 earthquake came without warning. Geophysicists hope the next one will not.

Egypt is divided into three seismic zones. Cairo is in the district deemed most at risk and most vulnerable to the destructive forces of an earthquake.

The building code until 1992 included safeguards but many were either insignificant or vague, and most were rarely implemented. Following the 1992 earthquake the government introduced tougher construction guidelines including seismic provisions.

Earthquake-proofing is now mandatory in new construction, at least officially. Existing structures can be strengthened with fibre-reinforced plastic or polymer – thin sheets that can be far stronger than steel once applied to columns, beams or brick walls.

"Unfortunately this material is very expensive and not locally produced," says Mourad. "It is used here mostly to wrap columns in office towers. In most cases the only feasible option for retrofitting is to drill through the brick and pour concrete, or to reinforce the structure with steel ties or bars."

Enforcement of new building codes too has been difficult. Litigation is slow, and a small bribe to the right official can make a hefty fine disappear. But there has been one incentive for compliance. "New buildings of significant value follow these codes to qualify for insurance," says Mourad. "If they don’t, they cannot get insurance."

In Cairo’s sprawling slums, however, most buildings are constructed without licence or insurance, and with little concern for building codes or safety measures. Many that were damaged in the 1992 earthquake and slated for demolition are still in use.

SCIENCE-EGYPT: Earthquake Fear Brings Tremors

By Cam McGrath Reprint | | Print |

Cam McGrath

CAIRO, Oct 17 2002 (IPS) - The tremors that rocked Cairo in August have left the city fearing for its future if another earthquake were to hit.
(more…)