Global Positioning System (GPS) and GPS-Acoustic Observations: Insight into Slip Along the Subduction Zones Around Japan

The global positioning system (GPS) is one of the most powerful tools available for observation of Earth's surface deformation. In particular, coseismic, postseismic, slow transient, and interseismic deformation have all been observed globally by GPS over the past two decades, especially in subduction zones. Moreover, GPS-acoustic techniques have been developed for practical use in the past decade, allowing observation of offshore deformation immediately above slip regions. Here, we describe the application of GPS and GPS-acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around Japan, where geodetic data coverage is particularly dense. The data demonstrate temporally variable strain accumulation in the source region of the 2011 Mw 9.0 Tohoku-oki earthquake, and observation of the huge slip of the Tohoku-oki earthquake near the trench using GPS-acoustic methods has considerably advanced our knowledge of stress release and accumulation in this subduction zone.