Tectonic wobbles recorded by GPS displacements in Japan before the Tokoku Oki Earthquake in March 2011. Left: Horizontal displacements show eastward and westward movement of Japan in the six months prior to the earthquake. Right: Vertical displacements show upward and downward motion. While the displacements are small (approximately one-quarter of an inch), they give geologists important clues about the processes that weaken the subduction zone fault prior to large earthquakes. Credit: Jonathan Bedford