Brian Kennett’s innovations in theoretical seismology, as well as his profound and wide-ranging observational studies, have had a lasting impact in geodynamics and geochemistry and have significantly improved the practice at international data centers for seismology.
In Cambridge, where he obtained his Ph.D. in 1973, he developed the first method to compute complete seismograms in layered models with control of reverberations. He combined this with observational studies of seismic waves at intermediate and high frequencies—work that eventually led to the two-volume book The Seismic Wavefield. This is already a classic, broad in scope, encompassing near-field strong ground motions to wave propagation on a global scale. After moving to Australia, he pioneered, with Rob van der Hilst, the first continent-wide mobile array of broadband seismographs (SKIPPY).
Brian took the lead in constructing a reference Earth model that gave accurate predictions of the travel times of the seismic phases for earthquake source location. With Bob Engdahl he developed the iasp91 model and further improved this by the addition of new travel time data on core phases (ak135). These models are now used by most international organizations as standards for the routine determination of earthquake locations and by a number of research groups performing high-resolution seismic tomography using the travel times of seismic phases.
Of great importance has been his development of joint seismic tomography using the arrival times of both P and S waves to extract robust constraints on the distribution of bulk and shear moduli at depth. This work sparked an extremely productive effort among seismologists, mineral physicists, and geodynamicists to shed insight into the material nature of mantle heterogeneity. A lasting outcome from this endeavor is quantitative interpretations of 3-D Earth structure in terms of thermal and compositional variations of the mantle in their relevant phase assemblages that link seismic and geodynamic interpretations of Earth structure in a consistent way.
In addition to his scientific work, Brian has been a mentor of numerous seismologists and a leader of the international seismological community, as president of the International Association of Seismology and Physics of the Earth’s Interior; editor of Geophysical Journal International for 20 years, Physics of the Earth and Planetary Interiors, and Earth and Planetary Science Letters; and nationally as director of the Research School of Earth Sciences in Canberra.
—Guust Nolet, Université de la Cote d’Azur, Nice, France; also at Princeton University, Princeton, N.J.
It is a singular honor to be awarded the AGU Inge Lehmann Medal for the facets of my work connected with the deeper Earth. I thank my nominator, Guust Nolet, and my supporters for their efforts on my behalf.
My research has been primarily based in seismology, with both observational and theoretical components directed at the understanding of seismic wave trains. These studies have also involved occasional collaborative forays into mineral physics and geodynamics. I have tended to work on seismological results at higher frequencies with particular emphasis on fine structure within the Earth that is likely to have the closest relationships to geochemistry and petrology.
Most of this work has been undertaken at the Australian National University, where Ted Ringwood encouraged my early work on the mantle, though he did not always like the answers obtained. Thanks to the push by Anton Hales for improved seismic travel times, I collaborated with Bob Engdahl and Ray Buland on the development of models that are now used for routine location by major international agencies. With the availability of travel times that are consistent between P, S, and the depth phases, it is possible not only to get better locations, notably in depth, but also to generate improved phase readings that can underpin high-resolution tomographic imaging. Following reprocessing, the arrivals of both P and S waves can be exploited in joint tomography that allows the characterization of different heterogeneity regimes, as well as the delineation of major structures. With multiple images a more direct answer can be sought for the relative influences of temperature and composition.
New results frequently require a new approach. With Rob van der Hilst we established the first continent-wide mobile array in the SKIPPY experiment across Australia. Among many other results, intriguing evidence of high-frequency scattering in the inner core was brought to light in work with George Poupinet, thanks to a fortunate distribution of seismic events around Australia. Improved knowledge of shallow structure, utilizing adaptive stacking procedures and novel array designs, has also contributed to greater transparency for the influence of deep structure.
None of these efforts would have been possible without the unwavering support of my wife, Heather, my companion on a more than 40-year journey exploring the Earth in depth.
—Brian Kennett, Australian National University, Canberra