The quantity and quality of satellite-geodetic measurements of tectonic deformation have increased dramatically over the past two decades improving our ability to observe active tectonic processes. We now routinely respond to earthquakes using satellites, mapping surface ruptures and estimating the distribution of slip on faults at depth for most continental earthquakes. Studies directly link earthquakes to their causative faults allowing us to calculate how resulting changes in crustal stress can influence future seismic hazard. This revolution in space-based observation is driving advances in models that can explain the time-dependent surface deformation and the long-term evolution of fault zones and tectonic landscapes.
The next decade should see us begin to discriminate between earthquake models using more and better Earth Observation data that describe the evolution of deformation in space and time for an increasing number of earthquake faults. The models make specific predictions about the temporal and spatial behavior of deformation that can be discriminated with long time-series of observations. At the same time, complementary data from seismic imaging and rheological constraints from rock mechanics will be vital in solving this problem.
Satellite geodesy offers the opportunity to measure the complete earthquake cycle: first, coseismic slip in the seismogenic upper crust, its relationship with aftershocks and fault segmentation; second, postseismic deformation localized on fault structures as shallow and deep afterslip, or more widely distributed through the ductile lower crust and upper mantle flow as viscoelastic relaxation; and third, interseismic strain accumulation across fault zones between earthquakes. By using the high spatial and temporal resolution of satellite observations, it will become possible to determine the time-dependent rates of deformation as well as the spatial extent of shear zones and weak zones beneath faults. Improved measurements of these processes in time and space will allow us to better constrain the lateral variability and depth-dependent rheology within the crust.
On a broader scale, Earth Observation data are now reaching the spatial resolution and accuracy to enable us to assess the fundamental mechanics of how continents deform. We have known for decades that the continents do not deform as large rigid plates like the oceans, but the kinematics and dynamics of continental deformation are still unclear. The debate has historically been polarized between two end member views. In one, the continents have been considered to act like a viscous fluid, with internal buoyancy forces playing a key role in controlling the distribution of deformation, and faults only acting as passive markers reflecting the deformation of a deeper, controlling layer. The alternative view has been that the continents can be considered to be a collection of rigid blocks, each behaving in essence like an independent plate. Resolving this issue is important for earthquake hazard assessment–we need to understand the degree to which deformation and earthquakes are focused on the major, ‘block-bounding’ faults, as opposed to being distributed throughout the continents. Long time-series of surface deformation data from Earth Observation satellites will enable us to quantify the degree to which deformation occurs away from the major ‘block-bounding’ faults
Conceptual cartoon of deformation in the crust and uppermost mantle.