Few scientists’ work can honestly be claimed to have transformed the perception of how Earth works. If a picture is worth a thousand words, then it is true that Steve Grand’s tomographic images clearly resolving the subducted Farallon slab penetrating through the mid-mantle have transformed our understanding by demonstrating that Earth’s convective system necessarily involves the whole mantle. Steve, given his abundant modesty, would never ascribe to himself such an impact, but the vigorous debates that raged from the 1970s to the 1990s over layered versus whole-mantle convection were immediately put to rest with the 1994 publication, in the Journal of Geophysical Research, of his Atlantic-centered tomography that clearly revealed the Farallon slab at mid-mantle depths in both map and cross-sectional views. Of course, the iconic image that sealed the deal was the 1997 cover of GSA Today, “Global Seismic Tomography: A Snapshot of Convection in the Earth,” with Rob Van Der Hilst and S. Widiyantoro. To quote Dan McKenzie, “In my view he is the most wide ranging and careful observational seismologist now active.” In a fundamental sense, what characterizes Steve’s work throughout his career are two central components. First is the development and application of state-of-the-art tools to address first-order questions. Second is a remarkable ability to identify where to apply those tools to go after important problems that seismology can address using well-conceived and carefully executed analyses. Whether it is the clear imaging of the Farallon slab in the deep mantle, resolving the global distribution of density anomalies driving mantle dynamics, revealing the deep root of the Yellowstone plume, or remarkably detailed images of the mantle beneath eastern Asia, Steve has been a central driving force in bringing each of these endeavors to fruition. Together these advances have demonstrated Steve’s profound (literally and figurately) impact on seismology, both in global and regional tomography, and the Earth sciences writ large. Steve Grand has made critically important contributions to the understanding of the structure, composition and dynamics of Earth's mantle. It is therefore entirely fitting and appropriate that Steve receive the 2022 Inge Lehmann Medal from AGU. — David Rowley University of Chicago Chicago, Illinois

Thank you, David, for your kind citation. I was surprised, humbled and honored to hear that I had received the Inge Lehman Medal and greatly appreciate the effort that you and other colleagues made to advance my nomination. The list of previous Lehman Medal recipients is truly outstanding, but the first recipient, Don Helmberger, is especially noteworthy to me. Don was my adviser as a graduate student at the California Institute of Technology (Caltech). His unique approach to seismology was to assume every “wiggle” in a seismogram can be deterministically understood and modeled using synthetic seismograms, and that approach has guided me through my career. While at Caltech, we modeled seismograms sampling the upper mantle beneath North America that resulted in models still in use today, and the experience got me hooked on mantle seismic studies. I was lucky to start my career at the advent of global seismic tomography. I naively thought that I could go through individual seismograms to develop my own 3D seismic model of Earth’s mantle, not realizing the amount of time that I would end up pursuing this. A high point, however, was at the 1996 Gordon Research Conference, where Rob van der Hilst and I compared our independently derived tomography models and found general agreement between them beneath North America. Seeing ancient deep mantle slabs for the first time was exhilarating. Throughout my career I have been fortunate to have had excellent students, postdocs and colleagues whom I owe a lot to. I am particularly grateful to Alessandro Forte and Dave Rowley for a collaboration spanning 20 years. Alessandro convinced me to do joint inversions of seismic and geodynamic data that led to a deeper understanding of mantle dynamics as well as the geologic manifestation of deep mantle processes. I also need to thank Fenglin Niu and Jim Ni for guiding me in a number of field projects. The projects were productive but also a lot of fun. Over my career, our knowledge of Earth’s deep mantle has gone from a bland, uniform volume of remote rock to one populated by slabs and plumes as well as previously unimagined LLSVPs (large low shear velocity provinces), ULVZs (ultralow velocity zones) and deep mantle scatterers. It’s been a pleasure and honor to have been a part of that voyage of discovery. Though the advances have been remarkable, there is still much we don’t understand about the deep Earth, but I am confident many new discoveries are on the horizon. — Stephen Grand University of Texas at Austin Austin, Texas