Michael C. Gurnis
The 2013 Augustus Love Medal is awarded to Michael C. Gurnis for fundamental contributions to geodynamics through studies of subduction zone dynamics, mantle flow induced long-term sea-level variations, and the thermo-chemical nature of the lower mantle.
Michael Gurnis stands out amongst his peers as a geodynamicist who effortlessly crosses the boundaries between seismology, geodynamic modelling, and geological field observations. He has been a pioneer in research on the dynamics of subduction zones and long-term sea-level change. He developed novel numerical techniques and widely used community computer modelling software. In the early 1990s through a series of theoretical and computational models, Gurnis showed how mantle convection could be visibly expressed in eustatic and regional sea level change, building on previous models by Mitrovica et al. (1989). He demonstrated that changes in plate spreading could lead to vertical motions near subduction zones on a continental plate, that in a dynamic Earth, eustatic and epeirogenic motions should have approximately the same amplitude, and that fluctuations in the geoid were substantially less important than changes in dynamic topography.
His theoretical work was subsequently applied to the observed stratigraphic record in sedimentary basins in a series of collaborative studies not only by Gurnis and his collaborators, but also by other groups, demonstrating the broad impact his work has had on the geodynamics community. Gurnis developed novel dynamic models for the initiation of subduction using a method in which fault zones develop through failure of a visco-elastoplastic material. In models tailored to oceanic lithosphere, he explored the competing roles of thermal evolution, elastic bending, viscous mantle flow, and plastic failure. The models have found wide applicability to the Marianas and Tonga-Kermadec subduction systems.
Gurnis further showed that low viscosity wedges and channels above the subducting crust can have a substantial influence on subduction zone structure. Such models explain the poor correlation between traditional geodynamic controls, subducting plate age and convergence rates, on slab dip, thus yielding a major advance of our understanding of subduction processes. For example, such models shed light on puzzling flat subduction systems, like in Central Mexico, where there is no deformation on the overriding plate above the flat segment. The discovery of the post-Perovskite phase change, arguably the most fundamental discovery about the Earth’s lower mantle in the last 30 years, is another example of Gurnis’ originality and creativity.
Gurnis and his former student Sidorin were the first to propose such a phase change near the core-mantle boundary in a series of papers published around 1999, based on their joint geodynamic and seismological modelling of D”. Their studies provided important motivation for later mineral physics research that eventually confirmed the existence of this phase change in 2004. Taken together, the activities described above frame a career that has been marked by a long history of transformative contributions to global geophysics.
For his seminal, lasting contributions to our understanding of mantle structure and dynamics, and their relation to plate tectonics, dynamic topography and, more generally, the geological record, Michael Gurnis has earned inclusion among the list of recipients of the Augustus Love Medal.