SUBQUAKEX Projet

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Modeling Mega-Thrust Earthquake Dynamics and Subduction Seismic Cycle

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This post is being drafted …

The recent Japanese and Sumatra megathrust subduction earthquakes have caused dramatic economic and human losses. Understanding how these catastrophic natural events nucleate and generate crustal deformation faces several limiting factors; The difficulty to measure earthquake deformations undersea, investigating the deep source of earthquakes, and encompassing the time-scale extent of the seismic cycle which is far longer than the span of geodetic and seismological observations. Consequently, major scientific open questions remain regarding key deformation processes. Among those, how friction heterogeneity controls interplate mechanical coupling appears as a crucial issue. In many subduction zones, geodetic data reveal unexplained spatio-temporal slip patterns (slow sleep events, quiet seismic activity phases, etc.), sometimes preceding major earthquakes. The role of the brittle/ductile transition, which marks the down-dip limit of the seismogenic zone, on the seismicity and surface deformation pattern, is also poorly constrained.

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Figure 1: Slideshow showing different views of the 2D and 3D subduction zone experimental set-ups. From Caniven and Dominguez, (2021).

In the last decade, new experimental approaches emerged to investigate the physics of earthquakes (Rosenau et al., 2017, and references therein). Inspired by these pioneer studies, and following our previous works on the strike-slip fault earthquake model (Caniven et al., 2015, 2017), we developed a scaled analog model of a subduction zone to simulate megathrust events and realistic earthquake cycle phases. The subduction zone model shares the same multi-layered visco-elasto-plastic rheology as the strike-slip fault model, including the visco-elastic coupling between the crust and the mantle wedge.

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TIME LAPSE VIDEO …. Coming soon.

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Interseismic phase: During the interseismic period, the friction along the seismogenic zone (SZ) increases the mechanical coupling between the two plates, inducing a partial or total locking of the subduction interface. Consequently, slab continuous motion forces the upper plate (UP) to move in the same landward direction. UP horizontal displacements reach a maximum, equal to the slab subduction velocity, near the trench, then linearly decrease toward zero landward, indicating that elastic deformation is accumulating. Interestingly, despite the relative simplicity of the analog model, the interseismic phases exhibit notable kinematic variability. Episodic slip events are commonly observed along the SZ, except when the subduction interface is fully locked.

Coseismic phase: The incremental horizontal and vertical displacement fields and associated profiles exhibit an asymmetrical kinematic pattern. For large coseismic slip events, upper plate horizontal displacements increase rapidly seaward, reaching a maximum value (>500 microns) close to the trench. The vertical surface displacement component shows subsidence located trenchward of the SUTZ and above the deeper part of the SZ, and an uplift pattern above the upper part of the SZ. This pattern arises mainly from the interaction of several processes; 1) the deformation induced by the elastic rebound that compacts vertically the UP (subsidence) while it is stretched horizontally, 2) UP trenchward displacements along the 10-11° dipping plate interface that induce positive vertical motion (uplift), 3) the surface free edge effect which amplifies the uplift displacement near the trench.

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The model succeeds in replicating the strain field of all seismic cycle phases. The coseismic phase is characterized by dynamic fault ruptures presenting wide ranges of magnitudes, slip-velocities, and locations along the seismogenic zone. Episodic aseismic creep and slow-slip events occur during the main interseismic phase depending on the amount of frictional coupling along the seismogenic zone. As in Nature, quasi-instantaneous coseismic slips (duration < to 200 milliseconds) up to very slow-slip events (duration > tens of seconds) are observed in our experiments. The simulated postseismic deformation is also consistent with natural observations. It starts with after-slip propagating along the seismogenic zone immediately followed by visco-elastic relaxation, affecting the portion of the upper-plate resting on the ductile mantle wedge, induced by slow slip horizontal shearing at the foam-silicone transition. The visco-elastic coupling between crust and mantle induces a delayed release of elastic stress in the upper plate providing a realistic postseismic surface strain pattern consistent with available geodetic measurements.

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Learn more:

-> Caniven, Y., & Dominguez, S., 2021. Validation of a multi-layered analog model integrating crust‐mantle visco‐elastic coupling to investigate subduction megathrust earthquake cycle. Journal of Geophysical Research: Solid Earth, 126, e2020JB020342. https://doi.org/10.1029/2020JB020342 -> PDF

See also:

-> Caniven, Y., Dominguez, S., Soliva, R., Cattin, R., Peyret, M., Marchandon, M., Romano, C. and Strak, V., 2015. A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle. Tectonics, 34: 232–264. doi: 10.1002/2014TC003701.

-> Caniven, Y., Dominguez, S., Soliva, R., Peyret, M., Cattin, R., Maerten, F., 2017. Relationships between along-fault heterogeneous normal stress and fault slip patterns during the seismic cycle: Insights from a strike-slip fault laboratory model, Earth and Planetary Science Letters, Volume 480, Pages 147-157, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2017.10.009.