The role of space-based observation in understanding and responding to active tectonics and earthquakes

T he study of active tectonics is primarily concerned with the deformation of the Earth’s surface. This process results in the growth of mountains, rifting of continents and evolution of the geomorphic landscape. We aim to understand the material properties and processes that control the distribution of strain in the Earth’s crust, from mobile belts to rigid cratons. An important consequence of the movement of the Earth’s crust is that the slow accumulation of strain in the cold, brittle upper part of the crust (which builds up over hundreds to thousands of years) must eventually be released, often in earthquakes. Understanding the fundamental processes of tectonics will contribute to mitigating the growing risk of an increasingly urbanised population exposed to such hazards1. Earthquakes occur when the accumulation of strain in the interseismic period results in a level of stress that can no longer be supported by friction on the fault2. The long-term accumulated elastic strain is recovered in the coseismic event resulting in a net translation of material either side of the fault. There are two important and measurable outcomes of this sudden strain release. First, the transient excitation of elastic waves from the energy released, which propagate through the Earth as body waves or along the free surface as surface waves and can result in damage to buildings. These waves can be measured by seismometers globally, and can be used very quickly (o30min) to issue alerts on potential impact3. Second, the permanent displacement of the surface with respect to the far-field can be measured geodetically by methods such as triangulation and Global Navigation Satellite Systems (GNSS)4, and more recently by remote methods such as interferometric synthetic aperture radar (InSAR)5 and optically derived offsets6. DOI: 10.1038/ncomms13844 OPEN