Publication Date:
2023-01-21
Description:
An earthquake‐induced stress drop on a megathrust instigates different responses on the upper plate and slab. We mimic homogenous and heterogeneous megathrust interfaces at the laboratory scale to monitor the strain relaxation on two elastically bi‐material plates by establishing analog velocity weakening and neutral materials. A sequential elastic rebound follows the coseismic shear‐stress drop in our elastoplastic‐frictional models: a fast rebound of the upper plate and the delayed and smaller rebound on the elastic belt (model slab). A combination of the rebound of the slab and the rapid relaxation (i.e., elastic restoration) of the upper plate after an elastic overshooting may accelerate the relocking of the megathrust. This acceleration triggers/antedates the failure of a nearby asperity and enhances the early slip reversal in the rupture area. Hence, the trench‐normal landward displacement in the upper plate may reach a significant amount of the entire interseismic slip reversal and speeds up the stress build‐up on the upper plate backthrust that emerges self‐consistently at the downdip end of the seismogenic zones. Moreover, the backthrust switches its kinematic mode from a normal to reverse mechanism during the coseismic and postseismic stages, reflecting the sense of shear on the interface.
Description:
Plain Language Summary:
Subduction zones, where one tectonic plate slides underneath the other, host the largest earthquakes on earth. Two plates with different physical properties define the upper and lower plates in the subduction zones. A frictional interaction at the interface between these plates prevents them from sliding and builds up elastic strain energy until the stress exceeds their strength and releases accumulated energy as an earthquake. The source of the earthquake is located offshore; hence illuminating the plates' reactions to the earthquakes is not as straightforward as the earthquakes that occur inland. Here we mimic the subduction zone at the scale of an analog model in the laboratory to generate analog earthquakes and carefully monitor our simplified model by employing a high‐resolution monitoring technique. We evaluate the models to examine the feedback relationship between upper and lower plates during and shortly after the earthquakes. We demonstrate that the plates respond differently and sequentially to the elastic strain release: a seaward‐landward motion of the upper plate and an acceleration in the lower plate sliding underneath the upper plate. Our results suggest that these responses may trigger another earthquake in the nearby region and speed up the stress build‐up on other faults.
Description:
Key Points:
Seismotectonic scale models provide high‐resolution observations to study the surface deformation signals from shallow megathrust earthquakes.
Surface displacement time‐series suggest a sequential elastic rebound of the upper plate and slab during great subduction megathrust earthquakes.
Slip reversal may be caused by rapid restoration of the upper plate after overshooting and amplified upper plate motion.
Description:
SUBITOP Marie Sklodowska‐Curie Action project from the European Union's EU Framework Programme
Description:
Deutsche Forschungsgemeinschaft
Description:
https://doi.org/10.5880/fidgeo.2022.024
Keywords:
ddc:551.22
;
analog modeling
;
megathrust earthquake
;
seismic cycle
;
elastic rebound
;
upper plate
;
overshooting
Language:
English
Type:
doc-type:article
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