Leonard Huxley Lecture Theatre
Professor Brian Kennett
Research School of Earth Sciences
Probing Subduction zones:
Seismic wave propagation and tomography
Most of the world’s earthquakes are associated with subduction zones where oceanic lithosphere descends into the Earth beneath an overriding plate. Growth of the sea floor through spreading at mid-ocean ridges is accommodated by recycling through the subduction process. The descending material is colder than its surroundings and the consequent variations in physical properties can be captured through their effects on the passage times of seismic waves between sources and receivers. Such seismic tomography is well suited to delineating the zones of faster wavespeed associated with the subducted plate. By exploiting both compressional (P) and shear (S) waves we changes can be recognised within the subducting material that may, e.g., influence the behaviour of great earthquakes such as Sumatra-Andaman in 2004 and Tohoku-oki in 2011.
The subduction zones also carry high frequency energy from deep earthquakes to the surface and cause significant ground shaking well displaced from the source. Such energy would be expected to be rapidly shed from the zone of fast wavespeeds, but internal heterogeneity elongated along the plate is sufficient to trap the energy and bring it to the surface from even events as deep as 500 km. The guided waves are disrupted if the properties of the slab change, and provide useful probes to understand features in tomographic images.
Brian Kennett FAA FRS is currently Distinguished Professor of Seismology at the Research School of Earth Sciences, The Australian National University. His research has covered a very wide range of topics in seismology, from reflection seismology to studies of the deep Earth and from theoretical to observational studies. He has received recognition through many medals and awards including the Gold Medal in Geophysics from the Royal Astronomical Society, the Gutenberg Medal from the European Geosciences Union, the Murchison Medal from the Geological Society of London, and the Jaeger and Flinders Medals from the Australian Academy of Sciences. He is a Fellow of the Australian Academy of Sciences and the Royal Society (London).