When the Earth quakes

Every day, thousands of earthquakes take place all over the world. Most of them can hardly be noticed, but now and again, they really go off with a bang. When that happens, it is a busy time for earthquake scientist Kuvvet Atakan and his colleagues in the Norwegian National Network for Earthquake Research at the University of Bergen.

Kuvvet Atakan is one of those people who are always at work; earthquakes do not respect normal working hours. When there was an earthquake on the Norwegian island of Sotra on December 8 last year his phone was rung off its hook in the middle of the night by the media, the police and ordinary members of the public. He was interviewed in front of the TV2 cameras while he logged on to the University of Bergen's computer system from his house in order to keep an eye on the earthquake.

Kuwet Atakan registers earthquakes from all over the world at the University of Bergen's Seismological Observatory.

The seismology group at the University's Department of Solid Earth Physics carries out a wide range of tasks. The scientists do research on earthquakes, develop earthquake measurement technology and have responsibility for keeping the public informed. The Seismological Observatory in Bergen operates 23 seismographic stations all over mainland Norway and at Ny Ålesund on Spitzbergen and on the islands of Bjørnøya and Jan Mayen. The Seismological Observatory records movements of the Earth's crust 24 hours a day. In our part of the world earthquakes are few and weak. The Sotra earthquake was quite noticeable, but even so it was fairly innocent. This is not the case in many other parts of the world.

Equivalent to 32 Hiroshima bombs

In November 1999 Kuvvet Atakan was in Turkey, his native country, in connection with the catastrophic earthquake that had taken place in August that year. Earthquake research is thoroughly global in nature, and seismologists from several different countries had gathered to discuss the earthquake. Then it happened again! Buildings fell like flies and the landscape moved five metres at a speed of four kilometres a second. Atakan was shaken, quite literally. It is one thing to do research on earthquakes from your office; being caught in the middle of one is a different matter.

"You can study earthquakes from a scientific point of view at a high level, without ever getting to feel what the real thing is like. It is only when you find yourself in the middle of one that you realise the sort of forces that are set in motion during an earthquake, and just how small a human being is", he says.

The Turkish earthquake in August 1999 measured 7.4 on the Richter Scale.

"This earthquake caused a surface rupture along a fault that was 150 kilometres long and 17 km deep. The November quake was a bit weaker - 7.1, but even such a quake is incredibly powerful. We can compare an earthquake with the Hiroshima atomic bomb. An earthquake measuring 6.0 on the Richter Scale is equivalent to a single Hiroshima bomb; one at 7.0 releases about the same amount of energy as 32 such bombs", says Atakan.

Every year, on average, there are18 earthquakes between 7.0 and 8.0 somewhere in the world.

In november 1999 Kuvvet Atakan experienced a powerful earthquake at close hand when he was taking part in a conference on earthquakes in Turkey, his native country. Photo: Kuvvet Atakan.

"So far this year there have been two quakes of this magnitude on land; one in India and one in El Salvador. There were a total of six such quakes in January and February, but most people do not hear about these because they did not take place in areas where people live. The most powerful earthquake ever measured (in Chile in 1960) had a magnitude of 9.5. Earthquakes of this size are extremely rare, but quakes with a magnitude of 8.0 happen about once a year. These may create faults more than 300 km long. Luckily, they usually take place in unpopulated areas, e.g. in the mountains or under the sea.

Forces deep within the Earth

Earthquakes take place as a results of stresses in the Earth's crust.

"When these stresses are too great for a bedrock to withstand, a rupture or "fault" is the result. Such stresses are built up deep inside the Earth by a complex interplay of forces.

"If we look at a cross-section of the Earth, we find the solid Earth's crust outermost and the soft mantle layer underneath it.

The upper layer of the Earth consist of the huge tectonic plates of the Lithosphere. The largest of these is about the size of the Pacific Ocean and they may be up to 100 or 150 km thick. These plates are in continuous movement. Some of them are moving away while others are coming into contact with yet others. Either they collide or one of the plates is pushed beneath the other. When a plate moves into the vicinity of the hot mantle, it melts and creates new material that appears again in the form of volcanoes. Of course, this process can only be observed in geological time, that is, in the course of millions of years", says Atakan.

It is not just by chance that we only have a few relatively weak earthquakes in Scandinavia, while countries in Central America are often hit by them.

"Earthquakes occur in regions in which the plates are in contact with each other. Most earthquakes take place all around the Pacific Ocean. Another area is near the Aegean Sea. Norway lies far from the edges of tectonic plates, and changes in the Earth's crust take place very slowly around here. There are more than 100 years between earthquakes that measure more than 5.5 or 6.0. The last one was in the Oslofjord in 1904", says Atakan.

Most earthquakes take place somewhere within the Earth.

"When the rupture occurs, energy is released in the form of seismic waves that propagate through layers of rock to the surface. It is these waves that the seismograph stations register. The seismographs record the direction in which the wave is travelling, and the time at which it reaches the station. Measurements of the same quake made by different stations enable us to pinpoint the focus of the earthquake by taking cross-bearings of the measurements", explains Atakan.

Seismographs are sensitive instruments. The seismograph station installed in the University's Natural Sciences Building can record a quake as far off as Australia if it is strong enough. Because the Earth's crust in Norway is dense and homogeneous, local earthquakes as weak as 2.5 can be felt by people.

Mapping history

It was the American seismologist Charles Richter who developed the scale that measures the strength of earthquakes in 1935.

"Today, we use a scale which is physically related to to the size of the rupture in in the rock, and which is called "moment magnitude". A seismometer is placed below the surface of the Earth and is connected to a seismograph which monitors movements of the Earth. Seismologists used to have to work out manually where the earthquake had occurred, but now computers have taken over the calculations", says Atakan.

The seismograph registers eartquakes all over the world. Several thousand quakes take place every day.

There are historical reasons for the presence of the Seismological Observatory in the University of Bergen. It is thanks to the personal interest of the scientist Carl F. Kolderup that the first seismometer in Norway was located in Bergen Museum in 1905.

"Another of our tasks today is to do research on the history of earthquakes. Before the seismograph had been invented, scientists collected local tales of earthquakes. Kolderup was among those who collected such information and published them in Bergen Museum's Annual Reports. Now we can interpret these reports in the light of present-day knowledge and work out roughly how powerful these quakes were", says Atakan.

However, contemporary earthquakes are the most important field of effort for the staff of the Seismological Observatory.

National task

"So far, operation of the network has been mainly financed by the Norwegian Association of Petroleum Industry Operators, who find earthquake monitornig particularly useful because of their platforms in the North Sea. Just before last Christmas we signed a new seven-year contract. The agreement means that the petroleum industry's share of support for the operating costs of the network will gradually be reduced, while the University of Bergen's share will increase", says Atakan.

"As well as operating the network we also do research at international level. We have recently been awarded two new EU projects that will involve mapping active faults in regions with apparently low levels of seismic activity and testing out a method that will be used to determine the response of sediments to earthquake waves. This will mean developing software and carrying out experiments in specific areas. We operate completely independently of political and geographical borders. In order to be able to act when an earthquake takes place we have to keep ourselves at the frontiers of research", says Atakan, who emphasises that the job of operating the Seismological Observatory was self-imposed by the University of Bergen.

"In a longer-term perspective it would be desirable for the authorities to get involved and provide some support for operation of the network. After all, it is a national responsibility to carry out earthquake measurements in one's own country. When something does happen, we have to act quickly, and that means having sufficient resources available. It is not very likely that a catastrophe will take place in Norway, but we can never be quite certain that it will not. Earthquakes with a magnitude of 6.0 are not inconceivable. I sometimes ask myself whether we at the University or in society in general are ready to deal with such an earthquake. I don't believe that we are".

Unpredictable

At present, it is impossible to predict where or when an earthquake will occur.

"I often ask myself what I as a scientist can offer. In India, more than 20,000 people died recently in earthquakes. It is terrible that we cannot tell when another earthquake will take place. What we do know is that earthquakes do occur at more or less regular intervals along the same fault. In Turkey there have been several earthquakes along the North Anatolian Fault Zone.

There is every reason to believe that there will be a new earthquake in Istanbul within the next 30 years. The tragedy is that even though people realise this, it is difficult to react accordingly. A simple calculation suggests that about one million people are at risk from the next earthquake", says Atakan.

"It would be an impossible task to protect all the buildings in Istanbul. Construction codes are adequate, but inspections are poor and we know that both politicians and construction companies evade them. Politicians think according to a time horizon of four years, but earthquakes have a much longer perspective. Our responsibility as scientists must not be limited to obtaining research results. We need to participate actively in the process of implementing our results in real life. What will have been done in Istanbul in 30 years? Only the next catastrophic earthquake will tell".