A new journey to the Earth's inner core: a planet within the planet
Eighty-six years have passed since discovering the Earth’s inner core and more than fifty years since our first journey to the Moon. Meanwhile, global seismology has come a long way in providing insights into Earth’s internal structure and dynamics. However, progress in imaging the Earth’s inner core – a planet within the planet – has been impeded by the lack of geometric coverage of body waves from large earthquakes. Only recently, we started probing the inner core with probabilistic tomography and confirmed its innermost part containing distinct seismic anisotropy. In seeking the ways forward, we started experimenting with earthquake coda correlation. This contributed to the rise of a new paradigm – the coda-correlation wavefield. The first applications proved the inner core’s solidity by unambiguous detection of shear waves and anisotropy in shear. As I hope to demonstrate in this lecture, the coda-correlation studies may play a central role in global and planetary seismology in the coming decades.