Preface: New challenges for tsunami science: understanding tsunami processes to improve mitigation and enhance early warning

[...]dense networks of GPS sensors, such as the GeoNet network deployed in Japan for many years, open the possibility to provide a real-time detection of the coseismic deformation independently of the seismic data (see the paper in this SI by Hoechner et al., 2013). When coupled to a tsunami model, implying a slip inversion in this study, the a posteriori analysis show that such an early warning technique would have provided the maximum warning level for the coasts of the Tohoku area within 180 s of the 2011 rupture. In the future, the improvements of real-time GPS data processing, associated with a densification of the GPS coastal networks, may offer a promising perspective for warning systems monitoring large submarine earthquakes. All the suggested techniques aim to distinguish the tsunami signal from the ambient wave background, which can be highly elaborated due to the impact of tides, infra-gravity waves, seiches, storm surges, storm waves, and ship wakes.