| Abstrakt: |
Subduction zone accretionary prisms are commonly modeled as elastic structures where permanent deformation is accommodated by faulting and folding of otherwise elastic materials, yet accretionary prisms may exhibit other deformation styles over relatively short time scales. In this study, we use 6.5‐year (2014–2021) Sentinel‐1 interferometric synthetic aperture radar (InSAR) time‐series of post‐seismic deformation in the Makran accretionary prism of southeast Pakistan to characterize non‐linear viscoelastic deformation within an active accretionary prism on short timescales (months to years). We constructed a series of 3‐D finite‐element models of the Makran subduction zone, including an accretionary prism, and constrained the elastic thickness of the upper wedge and the flow‐law parameters (power‐law exponent, activation enthalpy, and pre‐exponential constant) of the lower wedge through forward model fits to the InSAR time‐series. Our results show that the prism is elastically thin (8–12 km) and the non‐linear viscoelastic relaxation of the deep portions of the prism alone can sufficiently explain the post‐seismic surface deformation. Our best fitting flow‐law parameters (n = 3.76 ± 0.39, Q = 82.2 ± 37.73 kJ mol−1, and A = 10−3.36±4.69) are consistent with triggering of low temperature dislocation creep within fluid‐saturated siliciclastic rocks. We believe that the fluids necessary for this weakening originate from sedimentary underplating and/or the presence the hydrocarbons. The presence of power‐law rheology within the lower wedge impacts the estimated plate coupling and the stress state in the subduction system, with respect to the conventional elastic wedge model, and hence should to be considered in future earthquake cycle models. Plain Language Summary: Following large earthquake ruptures, the Earth's surface can continue to deform for several years. The spatial and temporal pattern of this post‐earthquake surface deformation is related to the material properties beneath the Earth's surface. By modeling this deformation, we are able to infer the mechanical behavior of the Earth at depth (i.e., whether it behaves like a solid or a fluid, or something in between), which has important implications for assessing the seismic hazard in the region. In 2013, a Mw7.7 earthquake occurred in the Makran accretionary prism in southern Pakistan. We use satellite images to measure and monitor the surface deformation 6.5 years following the earthquake. We find that this deformation is mainly caused by the viscoelastic relaxation, a flow‐like behavior, of the lower prism material between 12‐ and 40‐km depth. This behavior likely results from the high fluid content within the accretionary prism. Key Points: We use finite element forward models to simulate the 6.5‐year interferometric synthetic aperture radar deformation time‐series following the 2013 Baluchistan earthquakeNon‐linear viscoelastic relaxation within the lower Makran accretionary prism dominates the post‐seismic deformationThe inferred flow‐law parameters suggest low‐temperature dislocation creep within the accretionary prism under fluid‐saturated condition [ABSTRACT FROM AUTHOR] |
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