Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles

Abstract

The behavior of the shallow portion of the subduction zone, which generates the largest earthquakes and devastating tsunamis, is still insufficiently constrained. Monitoring only a fraction of a single megathrust earthquake cycle and the offshore location of the source of these earthquakes are the foremost reasons for the insufficient understanding. The frictional‐elastoplastic interaction between the megathrust interface and its overlying wedge causes variable surface strain signals such that the wedge strain patterns may reveal the mechanical state of the interface. To contribute to this understanding, we employ Seismotectonic Scale Modeling and simplify elastoplastic megathrust subduction to generate hundreds of analog seismic cycles at a laboratory scale and monitor the surface strain signals over the model's forearc across high to low temporal resolutions. We establish two compressional and critical wedge configurations to explore the mechanical and kinematic interaction between the shallow wedge and the interface. Our results demonstrate that this interaction can partition the wedge into different segments such that the anelastic extensional segment overlays the seismogenic zone at depth. Moreover, the different segments of the wedge may switch their state from compression/extension to extension/compression domains. We highlight that a more segmented upper plate represents megathrust subduction that generates more characteristic and periodic events. Additionally, the strain time series reveals that the strain state may remain quasi‐stable over a few seismic cycles in the coastal zone and then switch to the opposite mode. These observations are crucial for evaluating earthquake‐related morphotectonic markers and short‐term interseismic time series of the coastal regions.

Postseismic backslip as a response to a sequential elastic rebound of upper plate and slab in subduction zones

“…We select only the analog events from the seismically steady-state stage for our analysis. Upper plate faults (in our case, a single backthrust fault) gradually emerge self-consistently downdip and up-dip of the main slip patches and accommodate plastic upper plate shortening over seismic cycles, as documented in earlier studies (Kosari et al, 2020(Kosari et al, , 2022aRosenau et al, , 2010Rosenau et al, , 2019.…”

“…In the presented 3-D experimental setup modified from Rosenau et al (2019) and introduced in Kosari et al (2020Kosari et al ( , 2022a, an ocean-continent subduction forearc model is set up in a glass-sided box (1,000 mm across strike, 800 mm along strike, and maximal 300 mm deep) with a 15° dipping, elastic basal rubber conveyor belt hereafter "model slab") driven at a constant rate by a DC motor via lateral rollers., normal to a rigid backwall. A flat-topped velocity neutral wedge made of an elastoplastic sand-rubber mixture (50 vol.% quartz sand G12: 50 vol.% EPDM-rubber) is sieved into the setup representing a 240 km long forearc segment from the trench to the volcanic arc (Figures 1).…”

“…The wedge itself and the conveyor belt respond mainly elastically to these basal slip events, similar to crustal rebound during natural subduction megathrust earthquakes. Over the course of the experiment, the experiments evolve from an initially "aseismic stage" to a "seismic" steady-state (Kosari et al, 2022a;Rosenau et al, 2019). We select only the analog events from the seismically steady-state stage for our analysis.…”

“…This study aims to address the sequential upper plate and slab elastoplastic-frictional response during the coseismic shear-stress drop and its early postseismic stage in a subduction megathrust system by employing a series of carefully monitored analog modeling experiments. Seismotectonic Scale Modeling can examine elastic and permanent deformation and investigate the interplay between short-term and long-term deformation signals in 3-D (Kosari et al, 2022a;. To examine the short-term feedback relationship between the upper plate and the slab, we explore two generic seismotectonic models representing seismically homogeneous and heterogenous subduction megathrust systems and capture the Ruff and Tichelaar, (1996).…”

Uplifted Pleistocene Marine Terraces at Active Margins: Modeling Reveals the Effects of Sea Reoccupation and Coseismic Uplift on Uplift Rate Calculation

“…It must be noted that our model runs a simplified seismic cycle, where coseismic vertical motion has positive sign and no interseismic deformation occurs. However, the assumption of a one‐way motion is increasingly being contradicted by new observations at subduction margins showing us that subsidence can characterize both the coseismic and the interseismic phase (e.g., Clark et al., 2017; Kosari et al., 2022; Ragon & Simons, 2023). Such motion is observed instrumentally, with rates up to −3 mm/yr (e.g., Alatza et al., 2020, http://www.egms.land.copernicus.eu), and geologically, at the Myr‐timescale, where subsidence seems to interrupt periods of uplift, albeit at lower rates (e.g., Menant et al., 2021).…”