Research in the geological sciences has been increasingly focused on the interactions between physical, chemical, and biological processes related to the evolution of the Earth. This systems-oriented approach differs from the period of verification that followed the discovery of plate tectonics, when the main thrust of research was to understand the mechanisms driving the plates. While much current research is still related to understanding the consequences and dynamics of plate tectonics, an equally important goal of modern geological sciences is to understand how physical, chemical, and biological phenomena operating at differing spatial and temporal scales interact.


Mid-ocean ridge research is at the forefront of systems-oriented studies in the earth sciences. Mid-ocean ridges are the primary sites for transferring energy and material from the Earth's interior to its surface. The global heat budget is dominated by the formation, cooling, and eventual subduction of oceanic lithosphere. The bulk of the planet's magmatic budget is accounted for by the generation of 20 cubic kilometers of new oceanic crust per year. Hydrothermal circulation that accompanies magmatism facilitates chemical exchange between the solid earth and the ocean and plays a pivotal role in supporting the unique biological communities that congregate along ridge axes. To understand the dynamics of mid-ocean ridges and the system as a whole we need to investigate interacting processes, such as magmatic, tectonic, and hydrothermal activity, over a range of spatial and temporal dimensions.


The purpose of my research is to place quantitative constraints on the physical structure of mid-ocean ridges and to use these constraints to infer the nature of magmatic, tectonic, and hydrothermal phenomena. To do so I use modern seismic methods, many of which I develop, to map internal structure on scales ranging from hundreds of meters to hundreds of kilometers. By mapping features over a range of scales we may determine, for example, the volume of upper mantle involved in decompression melting beneath ridges, the nature of the transition from broad scale upwelling (hundreds of kilometers) to the accretion of new crustal material within a kilometer-wide neovolcanic zone, the size and shape of axial magma chambers responsible for the formation of oceanic crust, and the spatial connections between hydrothermal cells and their crustal heat sources. Because mid-ocean ridge characteristics vary dramatically with magma supply (which loosely parallels spreading rate), my studies are conducted at a variety of geographic locations, including the slow-spreading Mid-Atlantic Ridge, the fast-spreading East Pacific Rise, sub-aerial sections of the ridge in Iceland, and exposed sections of oceanic crust and mantle found in ophiolites (Oman). Comparative studies of ridge segments in different stages of their evolution also assists in inferring temporal variability of long-lived geologic phenomena. The tomographic image of the East Pacific Rise at the left shows anomalous compressional wave velocities associated with axial magmatism.

Ocean Bottom Seismology

Seismological studies of mid-ocean ridges are entering a new era due to technological advances in ocean bottom instrumentation. In the past, ocean bottom seismometers were limited to a deployment duration measured in weeks. With advances in computer hardware and instrument design, a new generation of instruments will achieve deployment times measured in months and years. These advances are opening up new avenues for seismologists, including long-term monitoring of seismicity and passive teleseismic imaging of deep earth structure. Because my studies have pioneered the use of ocean bottom seismic arrays to characterize axial seismicity and to image three-dimensional physical structure, I am particularly excited by these developments.