Michael Clark

PhD thesis: Mapping Ultra-Low Velocity Zones (ULVZs) using Seismic Postcursors

2900km below our feet, at the core-mantle boundary, lie mysterious features called Ultra-Low Velocity Zones (ULVZs). These are thin regions, often hundreds of kilometres wide but only a few tens of kilometres thick, whose existence has been demonstrated by the way seismic waves slow and scatter as they pass through them. The composition and origin of ULVZs remain uncertain – they may represent regions of iron enrichment, remnants of an early molten layer or accumulations of subducted tectonic plates. ULVZs often cluster beneath Africa and the Pacific, and underneath volcanic hotspots such as Hawaii and Samoa, suggesting they may influence where plumes rise and volcanoes form. My research focuses on analysing specific types of seismic waves that skim along the top of the Earth’s core allowing me to systematically detect and map ULVZs worldwide, helping reveal how the Earth’s deepest structures shape surface volcanism, mantle circulation and the planet’s long-term evolution.

Who or what inspired you to pursue your research interests?

Before coming to Cambridge, I completed an MSci in Earth and Planetary Science at Imperial College London, where I discovered a passion for research and seismology. For my Masters project, I analysed seismic data from NASA’s InSight mission—the first working seismometer sent to Mars—to study a region of the Martian crust that is rifting apart. From this, I was able to learn about ongoing processes occurring beneath the surface of a planet 225 million kilometres away from us! This experience revealed to me the power of seismology and inspired me to pursue a PhD exploring the Earth’s interior.