BBC Horizon - Earthquake Storms (2003)

Earthquakes are among the most devastating natural disasters on the planet. In the last hundred years they have claimed the lives of over one million people. Earthquakes are destructive mainly because of their unpredictable nature. It is impossible to say accurately when a quake will strike but a new theory could help save lives by preparing cities long in advance for an earthquake.

“We knew that Izmit was dangerous”

Prof Geoffrey King, Institut de Physique du Globe

The surface of the Earth is made up of large ‘tectonic’ plates. These plates are in slow but constant motion. When two plates push against each other friction generates a great deal of energy. For this reason earthquakes occur most frequently on tectonic fault lines, where two plates meet. However these fault lines run for thousands of kilometres; predicting exactly where a quake will occur is nearly impossible.

Stress lines

In 1992, Dr Ross Stein was monitoring a large earthquake in a town in California called Landers. Three hours later, there was another quake 67km away at Great Bear. Stein believed that this was not simply an aftershock, instead he theorised the event at Landers had set off the earthquake at Big Bear. Stein believes that when an earthquake occurs the stress that has built up along the fault, is in part, transferred along the fault line. It is this energy transfer that causes other quakes to occur hours, days or months after the original.

Stein’s team began to look for connections between the quakes in Landers and Big Bear. They had already been working on a computer model that could help them study the relationship between earthquakes. The data collected during the Landers/Big Bear quake had enabled them to create a model that could predict where the stress from Landers would have been transferred. When they looked at the result the calculations did indeed show that the stress from Landers would have been transferred along the fault to Big Bear. They then plotted all of the subsequent ‘aftershocks’ and discovered that almost all occurred within a high-risk area they called a `red zone’. This did not prove the theory of earthquake storms though. In order to do that the quakes would have to be triggered months or even years after the original earthquake.

Scientists from around the world were attracted by this new theory and there was one part of the world where it seemed from the available evidence that the earthquake storm theory might hold true.

Tremor trail

Prof Geoffrey King was fascinated by the cyclic behaviour of the North Anatolian fault in northern Turkey. Earthquakes in the region moved from east to west with a period of quiet at the end before the cycle began again. King used the same model that had been used to show the connection between the quakes in Landers and Big Bear. The first earthquake King looked at was in the northern city of Erzican in 1939. Using the available data on that quake he found that a town to the west called Tokat was in the red, danger zone. Tokat was indeed struck by a quake in 1942. The model seemed to be working. In 1967 Adapazari, also in a red zone, was hit. It looked like stress generated in one earthquake was being transferred to the west. These could not be aftershocks as they were separated by years, not hours.

As King continued to put data into the model he discovered that a city called Izmit seemed to be the next place that would be struck. With a population of 500,000 people King and other scientists knew they needed to make this discovery public knowledge.

“Buildings can be improved. Construction can be modified”

Prof Geoffrey King

Newspapers, science journals and other publications all printed this remarkable news. Unfortunately there was not enough interest from the local community. In August 1999 King was tragically proved right when a massively energetic earthquake lasting just 45 seconds killed 25,000 people. It was a bittersweet feeling for King. On one hand he was proved right, on the other he knew that many people had lost their lives who could have been saved. King also knew that there was a high chance of more earthquakes. So using the data acquired from the Izmit quake he began to work out where the next most likely earthquake site would be.

The answer would cause a great deal of concern. At the edge of the red zone lay the city of Istanbul, home to more than four million people. The city’s high population density puts its inhabitants at maximum risk. There is good news though; if the warning from King’s team is heeded then arrangements can be made to make Istanbul safer in the event of an earthquake, whenever it happens. For now though, only time will tell if King’s prediction will prove correct.

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Pass: calek

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