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Abstract:
Understanding the along-strike seismogenic behavior of megathrusts is crucial to anticipating seismic hazards in subduction zones. However, if and how spatiotemporal frictional heterogeneity (high and low kinematic coupling) at depth feeds back into the upper-plate deformation pattern and how the upper-plate elastic signals and permanent records may correlate have yet to be fully understood. Hence, we mimic subduction megathrust seismic cycles using an analog seismotectonic model of an elastoplastic wedge overlying a frictionally heterogeneous megathrust. Coseismically, the zone above the down-dip limit of the aseismic and seismogenic patches undergoes extension and contraction, respectively, while the strain state shows a switch in polarity from coseismic to interseismic. The down-dip limit of the creeping zone produces permanent along-strike extension or contraction, depending on the frictional barrier strength. Our experiments show that the frictional locking heterogeneity generates more segmented along-strike strain patterns elastically (short term) than permanently (long term). Moreover, our results suggest that along-strike upper-plate strain patterns could serve as a proxy for interpreting persistent lateral variations of seismogenic behavior in subduction megathrusts.
