Abstract:

Despite considerable progress in global seismology, mineral physics, geodynamics, paleomagnetism, computational methods and mathematical geophysics, Earth’s core remains enigmatic. Progress in understanding the structure and evolution of the Earth’s inner core – a metallic ball about the size of Pluto – has been impeded by the lack of geometric coverage of seismic body waves due to an uneven global distribution of earthquakes and receivers. For example, only recently have we confirmed that its innermost part contains distinct seismic anisotropy. In seeking ways forward, we started experimenting with earthquake coda correlation by comparing digital waveforms recorded at different locations many hours after the onset of large earthquakes.

Applying the coda correlation principles proved the inner core’s solidity by unambiguously detecting shear waves spreading through it. Furthermore, we showed the existence of a low-velocity equatorial torus in the outermost outer core. We also showed that a single seismograph and global-scale waveform cross-correlations between seismic events (inter-source correlation) could be used to scan planetary cores. Using a growing number of global seismic stations, we observed up-to-fivefold reverberating waves from selected earthquakes along the Earth’s diameter, confirming a distinct anisotropy in the innermost inner core. I will review my group’s most important results and ambitions to date, with brief stops at the Earth’s centre and its various shells, the Outback, the Southern Ocean bottom, Antarctica and Mars. As I hope to demonstrate, the coda-correlation and similar innovative methods – apart from further development and the proliferation of seismic sensors – may play a central role in global and planetary seismology in the coming decades.

Speaker: Dr. Hrvoje Tkalcic (Australia National University)
 

 
Host: Christine Houser, ELSI.

Date:  Wed. 28 May 16:00-17:00 JST

Venue: Mishima Hall, ELSI