Over the years much has been learned about faulting and fault processes on land through the study of samples collects from exposed fault, ?fault rocks?. Measurements of fabric elements (such as grain orientation and sense of shear), deformation histories and properties such as strength and permeability have been the focus of research in many laboratories for decades, but owing to their inaccessibility, no such studies of fault rocks have been carried out. Using samples from a variety of sources including submersible sampling, drilling and ophiolites where oceanic rocks are exposed on land, this study will be the first of fault rocks from the seafloor. As a first venture into a new area of research it will face a number of difficulties, but will likewise almost certainly yield new insights. The broader impacts of this work are its contribution to fundamental knowledge, support for a young investigator, and support for a graduate student.
The world's oceans are floored by a crust that is quite different from the continents that most of us live on. The magnesium and iron rich basaltic crust is the product of delivery of mantle melts at mid-ocean ridge spreading centers. Though nearly two-thirds of the Earth's surface is formed at mid-ocean ridges, they are remarkably narrow, in the fast-spreading Pacific ridges less than a kilometer wide and in the slower spreading centers less than ten. Within the ocean crust are pillars of basalt, the sheeted dikes, that delivered melts into the crust, and are very impermeable; water does not flow easily through this layer. The Earth primarily cools and exchanges geochemical elements through the oceanic crust, and as the crust spreads off the ridges, it continues to exchange elements with seawater, including Carbon and metals, both important for society. And as the the ocean crust moves laterally over the Earth, earthquakes occur both in ridges, transforms faults, and within subduction zones, the latter posing great hazards to coastal cities. This project focused on the mechanics of faults that develop along mid-ocean ridges, but more generally how faults in oceanic crust behave. It turns out that contrary to a simple view of layered, undeformed rocks in the oceans, the crust there is instead typified by a complex network of fault zones across which crustal blocks rotated and moved. Central outcomes include a recognition that as the ocean crust fractures, the fractures and communited rock materials attain critical length scales that may govern the earthquake and permeability patterns that govern the oceanic crust. Experiments further showed that much of the material within faults in oceanic crust stabilize slip likely preventing earthquakes; this last conclusion explains an ongoing mystery about ocean crustal faulting wherein earthquakes are generally not observed in the sheeted dike complex and overlying basalts except near hydrothermal outflow zones, or vents. The project also established the tectonic environment of some noteworthy vents in the Caribbean, the deepest known. Lastly, the project offered an explanation for faulting events that do not produce earthquakes, but instead produce slow slip events. newly recognized phenomena that seismologists think may lead to understanding of devastating earthquakes confronting regions in the US Pacific Northwest.
