Seismologist Arwen Deuss uses large earthquakes to understand the structure of the earth and map variations in its composition and temperature. She has received an ERC grant of two million euros, for having a unique approach to measure the speed by using whole Earth vibrations, as well as determining the energy loss of such a wave, so called attenuation.
When an earthquake occurs on the other side of the world, Utrecht seismologists are able to measure it using their seismometers. For example, a major earthquake in Jakarta makes the earth ring like a giant bell, slowly expanding and contracting the earth. Dr. Arwen Deuss uses these vibrations to make images of the temperature and composition of the earth just as you might with a brain scan.
A dent in the church bell
As the earth is not a homogeneous mass, distorted vibrations make the Earth sound 'out of tune' as if there is a dent in the church bell. Because of these abnormalities, Deuss can precisely visualise the interior of the earth. “A homogeneous earth would produce images of one colour” says Deuss. “However, since the composition of the earth is varying everywhere, different colours are visible in these pictures.”
Slowdowns and speed-ups
Initially, a vibration which moves through the earth is only measured as it travels faster or slower. When a vibration moves through a warm medium, such as molten lava or a water pocket, the wave slows down. When travelling through a cold medium, it speeds up. In this way, you can roughly estimate the temperature and composition of the earth.
However, the signal also attenuates, which can be caused by a huge variety of factors. Analysing this is complex and there is virtually no one dealing with it. Deuss is the first in the world to start measuring attenuations using whole Earth oscillations. “Normally we only measure speed” says Deuss. “But the speed of the wave can have different causes. For example, if it travels through warm material or if there is iron present in the Earth. Speed alone does not give us enough information.”
“If we add the attenuation measurements” she adds, "the additional information will allow me to distinguish between temperature and material composition. If the oscillation is delayed as it passes through the hot part, strong attenuation occurs. But if it is delayed because it has moved through iron, there is no attenuation of the signal. Using this distinct difference, we can determine the temperature.