The 2015 Beno Gutenberg Medal is awarded to Göran Ekström for contributions to the understanding of the elastic (particularly anisotropic) and anelastic structure of the Earth, and for understanding and characterising seismic sources, especially unusual ones such as ‘ice-quakes’ or the Earth’s low frequency ‘hum’.
Göran Ekström is an exceptional seismologist in both creativity and productivity. Remarkably, his contributions cover a very broad range of interests, from global upper mantle tomography to the systematic study of earthquake moment tensors with inferences for seismo-tectonics, as well as, most recently, a focus on glacial earthquakes and their relation to climate change.
Ekström is perhaps best-known for his leadership of the Global Centroid-Moment-Tensor (CMT) project. CMT solutions are employed in practically all seismological research where knowledge of source parameters is needed and in nearly all studies of present-day tectonics. The moment magnitudes (Mw) from this catalogue have provided a key ingredient in the study of seismic risk under the Global Earthquake Model project. Ekström has been personally responsible for many developments in the method allowing the global threshold to be reduced to Mw=5, adding enormously to the size and utility of the catalogue. His development of a powerful low-frequency event-detection method has resulted in the discovery of ‘glacial earthquakes’, which are shedding new light on ice dynamics and temporal changes in glacial regimes. The method has also detected other ‘slow’ events, for example in mid-ocean ridge systems. He has also systematically studied non-double-couple volcanic events and recently used seismic waves from landslides to quantify their volume.
Ekström has made many important contributions to the determination of the Earth’s structure. A landmark study is the 1998 Nature paper in which the authors attracted the attention of the community to the intriguing radially anisotropic structure of the central Pacific upper mantle. This and other works, in particular on azimuthal anisotropy, have been used widely by mineral physicists and geodynamicists as constraints for physical and dynamical models of the upper mantle. Ekström has also had a long-standing interest in attenuation in the Earth. Recently, his group has produced the most up-to-date global upper mantle tomographic model of shear attenuation, using constraints from surface wave amplitudes. As is well known, attenuation is difficult to extract from amplitudes, few reliable models have been developed so far, and the authors have been able, for the first time, to make some inferences on the origin of differences in attenuation between continents and oceans.
In summary, Göran Ekström’s work is a pillar of modern seismology. His contributions to seismic sources and Earth structure are fundamental, his insight into seismic data is immense, and his passion for seismology is relentless.