Subduction zones host the largest earthquakes and associated tsunamis, but very little is known about how such earthquakes prepare. Understanding how such earthquakes get prepared and interact is a first order challenge in earth sciences.

To understand the nucleation of earthquakes, efforts are made to assess the relative contribution of foreshock seismicity versus aseismic pre-slip. To do that, most studies rely only on the analysis of seismological data and focus near the epicenter, and only a few weeks before the earthquake. However, subduction zones seem to be ruptured by sequences of large earthquakes. This represents a puzzling and unexplained observation and may imply that interactions exist at the scale of the subducting plate. More, the acceleration of the subduction prior to some recent megathrust earthquakes seems to be concomitant with an increase of seismicity deep in the slab ( 100km), but the physical mechanism responsible for these interactions still needs to be unveiled. These observations suggests that the subducting slab plays an important role, albeit downplayed, in the triggering of megathrust earthquakes.

Today, we are missing statistically significant observations of interactions between slow deformation and seismicity in the large subduction system. In DEEP-trigger, the challenge will be to analyse jointly the geodetic and seismological data that monitored recent earthquake sequences in South America, Japan and Sumatra. We will install dedicated geodetic and seismological stations at key areas in Chile and in Peru. Multi-scale observations of deformation and seismicity will be extracted from the great amount of geophysical data available. Supervised Machine Learning algorithms will serve to systematize, statistically depict these complementary observables, and to characterize how their empirical relationships evolve with time and space. Physical mechanisms driving the plate interface destabilization will be explored through mechanical and fluid modeling, and tested against the data.
The link between deformation and seismicity will be considered in the larger subduction system, and their potential role in pushing the megathrust interface to failure will be assessed through addressing the following questions:

1. At the scale of the seismic asperity, What is the link between aseismic slow slip and the seismic rupture, from short to long timescales ?
2. What is the role of deep processes and deep earthquakes in the initiation of megathrust ruptures?
3. What are the mechanisms of interations between earthquakes and deformation over the large scale? At the scale of the subduction zone, how distant changes transfer into large-scale deformation, potentially initiate slow slip and eventual rupture on the plate interface?

Updated on 23 April 2021