Towards imaging density using waveform tomography

Abstract

Nienke Blom studied methods to image variations in density inside the Earth using the technique of waveform tomography, a method based on modeling earthquake vibrations. Her work contributes towards better understanding the interior of the Earth, the dynamics of which drive everything that happens at the Earth's surface. As heavy material in the Earth sinks and light material rises, the Earth's internal structure constantly moves and changes at the speed of the growth of a finger nail. This has its effect on the outside: everything that happens at the Earth's surface -- the shape of continents, the occurrence of earthquakes and volcanism, but also the existence of a breathable atmosphere -- is a consequence of this constant motion. So far, however, it has been very difficult to image the variations in density that cause these motions in an independent and reliable way. During her PhD, Nienke Blom worked on developing ways to image these variations in density using the vibrations that are emitted from earthquakes. By modeling on a supercomputer how earthquake vibrations propagate through the Earth's interior, she deduced how the wavefield is altered by the presence of variations in density. Based on this, she developed a workflow to derive the structure of the Earth's interior from a comparison between measured seismograms and the modeled wavefield, which she is currently applying to the Eastern Mediterranean.