Periodic Reporting for period 4 - S-SIM (Sediments and Subduction Interface Mechanics: from micro-scale creep to global plate tectonics)
Período documentado: 2025-05-01 hasta 2025-10-31
Subduction zones-- where one tectonic plate dives beneath another-- produce the world’s largest earthquakes and tsunamis. Yet the same kind of plate boundary can behave very differently from place to place: some segments “lock” and rupture in major earthquakes, while others slide more quietly or produce slow, drawn-out events. A leading idea is that these differences depend on what is carried into the trench. Some margins subduct thick piles of sediments; others mainly subduct hard volcanic oceanic crust.
This project tested a simple but powerful hypothesis: the type of material entering a subduction zone-- especially sediments-- strongly influences both short-term slip behavior (including earthquakes and slow slip) and long-term mechanical behavior over millions of years. The project tackled this problem using three linked approaches: (1) studying naturally exhumed rocks that were once part of subduction interfaces, (2) laboratory experiments that measure how key rock types deform at high pressure and temperature, and (3) numerical models that connect rock strength and fault-zone structure to observable slip behavior and plate motions.
The primary outcome of the project is a coherent, physically grounded framework showing that subduction interfaces are not uniform faults: they are commonly mixed, finite-width shear zones in which the distribution of strong and weak materials and the movement of fluids play a first-order role in controlling plate-boundary strength and slip style (Fig. 1). This improves the physical basis for interpreting geophysical observations of active subduction zones and for understanding why seismic hazard varies along and between margins.
This project tested a simple but powerful hypothesis: the type of material entering a subduction zone-- especially sediments-- strongly influences both short-term slip behavior (including earthquakes and slow slip) and long-term mechanical behavior over millions of years. The project tackled this problem using three linked approaches: (1) studying naturally exhumed rocks that were once part of subduction interfaces, (2) laboratory experiments that measure how key rock types deform at high pressure and temperature, and (3) numerical models that connect rock strength and fault-zone structure to observable slip behavior and plate motions.
The primary outcome of the project is a coherent, physically grounded framework showing that subduction interfaces are not uniform faults: they are commonly mixed, finite-width shear zones in which the distribution of strong and weak materials and the movement of fluids play a first-order role in controlling plate-boundary strength and slip style (Fig. 1). This improves the physical basis for interpreting geophysical observations of active subduction zones and for understanding why seismic hazard varies along and between margins.
The project combined fieldwork, experiments, and modeling into a single workflow aimed at connecting real rock properties to real subduction behavior. Field and laboratory studies focused on three main regions that preserve exhumed subduction-interface rocks spanning a range of depths and conditions. Across these sites, we mapped deformation structures and analyzed microstructures to identify systematic differences between sediment-rich and basalt-rich parts of subduction interfaces. A key result is that deep interface deformation is often distributed across a zone rather than localized on a single sharp surface, and that the interface commonly contains a mixture of materials whose geometry and proportions matter mechanically.
In parallel, we carried out high pressure–temperature rock deformation experiments on minerals and rock types representative of subducted oceanic crust. A major outcome is a quantitative description of how important mafic assemblages deform under subduction-zone conditions, allowing direct comparisons to sediment-derived rocks. These experimental constraints translate “weak” and “strong” from qualitative labels into measurable parameters that can be used in models (Fig. 3).
We then developed numerical models at two scales. At the earthquake-cycle scale, models explored how a shear zone that is partly brittle and partly ductile, and that contains heterogeneity, can produce a range of transient slip behaviors, including slow slip. At the plate-tectonic scale, dynamic subduction models quantified how plausible variations in interface strength can influence slab motion, trench migration, and convergence rates (Fig. 2). Together, the modeling demonstrates that interface rheology and internal structure can control both short-term slip signals and long-term subduction dynamics.
The project’s results have been disseminated through peer-reviewed publications, conference presentations, invited talks, and open communication through the project’s public website. The main exploitation of the results is scientific: (i) providing quantitative constraints that can be adopted by the broader modeling community, and (ii) offering a clearer physical interpretation of geophysical signals (such as low-velocity layers and slow earthquakes) in terms of realistic rock types, fluids, and shear-zone architecture.
In parallel, we carried out high pressure–temperature rock deformation experiments on minerals and rock types representative of subducted oceanic crust. A major outcome is a quantitative description of how important mafic assemblages deform under subduction-zone conditions, allowing direct comparisons to sediment-derived rocks. These experimental constraints translate “weak” and “strong” from qualitative labels into measurable parameters that can be used in models (Fig. 3).
We then developed numerical models at two scales. At the earthquake-cycle scale, models explored how a shear zone that is partly brittle and partly ductile, and that contains heterogeneity, can produce a range of transient slip behaviors, including slow slip. At the plate-tectonic scale, dynamic subduction models quantified how plausible variations in interface strength can influence slab motion, trench migration, and convergence rates (Fig. 2). Together, the modeling demonstrates that interface rheology and internal structure can control both short-term slip signals and long-term subduction dynamics.
The project’s results have been disseminated through peer-reviewed publications, conference presentations, invited talks, and open communication through the project’s public website. The main exploitation of the results is scientific: (i) providing quantitative constraints that can be adopted by the broader modeling community, and (ii) offering a clearer physical interpretation of geophysical signals (such as low-velocity layers and slow earthquakes) in terms of realistic rock types, fluids, and shear-zone architecture.
The project advanced beyond the state of the art by directly linking three typically separate lines of evidence: the rock record of fossil subduction interfaces, laboratory measurements of rock strength under realistic conditions, and numerical models that translate those properties into observable behaviors. This integration matters because debates about why subduction zones differ often hinge on untested assumptions about material strength and fault structure.
Two key advances are (1) converting the mechanical behavior of important subduction-zone rocks into quantitative constraints that can be used in models, and (2) demonstrating that a finite-width, heterogeneous, fluid-influenced interface shear zone can naturally explain a wide range of observed slip behaviors without requiring a single “one-size-fits-all” fault model. This provides a more realistic foundation for future work that aims to connect geological materials and processes to seismic hazard.
Two key advances are (1) converting the mechanical behavior of important subduction-zone rocks into quantitative constraints that can be used in models, and (2) demonstrating that a finite-width, heterogeneous, fluid-influenced interface shear zone can naturally explain a wide range of observed slip behaviors without requiring a single “one-size-fits-all” fault model. This provides a more realistic foundation for future work that aims to connect geological materials and processes to seismic hazard.