The vast majority of catastrophic large earthquakes occur in subduction zones, and their timing and size is controlled by properties of the plate interface (coupling, fluid content). Processes in the downgoing slab of oceanic lithosphere (dehydration, stress distribution) are thought to also influence the plate interface. Both plate interface and slab are seismically active, and the constant background of 10s of thousands of microearthquakes every year contains abundant information on their state. Project MILESTONE is aimed at extracting this information by using state-of-the-art machine learning based tools to compile huge catalogs of microearthquakes from a set of subduction zones around the globe.
Microearthquakes on the plate interface appear to cluster around the edges of highly coupled regions, so-called asperities. This means that they can help us to map out the extents of possible future earthquakes, and different forms of seismicity (repeating earthquakes, swarms) can be used to infer the partitioning of energy between aseismic slip and stress buildup. We aim to move this direction of research forward by analyzing much larger set ofs events, collected at different plate interfaces, together with geodetic information. Microearthquakes inside the downgoing slab of oceanic lithosphere occur as a consequence of dehydration reactions along the path to higher pressure and temperature conditions. Locations and mechanisms of intraslab earthquakes can constrain slab geometries, temperature distribution, fluid budget and the evolution of the stress state in the oceanic lithosphere.
Results from MILESTONE have the potential to substantially improve earthquake hazard estimates along subduction zones. The obtained estimates of highly coupled regions can be used to generate shaking scenarios as well as tsunami simulations, which in turn can inform decision makers for concrete measures of disaster preparedness.
The overall objectives of the project are:
1) Understanding the relation between background microseismicity, interplate locking, megathrust earthquake ruptures and other plate interface processes. The use of "deep" seismicity catalogs of large subduction zone segments allows the delineation of stress accumulation at the downdip edges as well as along-strike separators of highly coupled regions on the megathrust (asperities).
2) Better defining what controls along-strike heterogeneity of interplate locking, and what physical processes are involved in its evolution. This can be achieved by looking for signatures of aseismic creep in the background seismicity (repeating earthquakes, swarms) and using these together with GNSS recordings to estimate the partitioning between seismic and aseismic motion along the megathrust as well as its temporal evolution.
3) Constraining the controls on style and abundance of intraslab seismicity and its variability along one subduction zone as well as between subduction zones.
4) Better understanding what mineral reactions may be involved in DSZ seismicity, and what the physical process of seismogenesis in the presence of fluids may be.
5) Better constraining the possible link between intraslab and megathrust seismic activity
