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Earthly power brought Jericho down

British Association's Festival of Science
The walls of Jericho fell not because of trumpet-playing inspired by the heavens, but by events beneath the ground, according to geologists who have pinned the calamity on an earthquake.

Now, the same unstable fault-line which demolished the Biblical city threatens the modern city of Beirut, which is hurriedly rebuilding itself after years of civil war, Dr Rob Butler of the University of Leeds told the British Association yesterday.

Excavations of ancient ruins in Israel and the Middle East over the past 20 years have established that a succession of cities there were destroyed by earthquakes, including Jericho, and then in 551 AD the Roman city which stood where Beirut does now.

"That was devastated either by an earthquake or a tsunami [the seawave caused by an undersea earthquake]," said Dr Butler. "The Roman columns collapsed and became the lower base on which the new town was built. Of course, columns are the worst thing to use for buildings in earthquake zones."

He also warned that "Beirut lies on a major active fault" and that the government of Lebanon is not taking enough care to build structures able to stand a devastating earthquake -which he reckons is inevitable.

"It may not be as high a risk as California or Tokyo, which are both in major earthquake zones. But they are building for that eventuality, whereas Lebanon is not," he said.

The fault-line is caused by a complex interaction of tectonic plates beneath the Earth's surface. It runs north from the Gulf of Arabia through the Dead Sea and up to the Mediterranean Sea. "Basically, the Red Sea is opening up, pushing Arabia northwards relative to Africa," Dr Butler explained.

At the points where the plates meet, they slide past each other - but not smoothly. When thousands of miles of opposing rock edges suddenly inch past each other, the resulting release of energy is felt as an earthquake.

At Easter, Beirut was rocked by a quake measuring 5 on the Richter scale. "They need to tighten up the building code - much of the rebuilding is on land reclaimed from the Mediterranean, with bulldozed rubble from the war zone. In an earthquake, unconsolidated ground can flow like liquid."

Spending a few million pounds on installing instruments to measure where smaller shocks occur would also help, he said. "Compared to the amount being raised on the stock market for rebuilding, it's a drop in a bucket."