What makes an earthquake big? In 2011, the North American and Pacific tectonic plates moved an unprecedented 50 meters in a matter of moments. This massive slip caused the tsunami that devastated communities in Japan, and it left clues that can help scientists understand how small earthquakes grow into great earthquakes. Immediately after a large earthquake, there is an opportunity to collect crucial information that can elucidate the properties behind these devastating events. As tectonic forces push the plates forward, friction on the faults holds them back. Earthquakes occur when the increasing local stress overcomes the frictional strength of a fault. The lack of measurements of the frictional force during this motion is one of the major impediments to progress in earthquake science. A deep borehole can access a fault and make essential measurements, but it must be drilled quickly, since many properties, such as the high temperature, are temporary. One year after the 2011 Tohoku earthquake, an international team of scientists and engineers mobilized to drill a borehole into the earthquake’s seismic slip zone. Operating from a ship in 7 kilometers of water, the expedition logged the fault, collected rocks, and installed an observatory in the fault zone. This session will present the initial results of the study and discuss characteristics of the fault zone, such as rock and fluid composition, architecture, and the nature of heat and pressure around the location of the earthquake slip.