Abstract
AbstractTension cracks were generated by past megathrust earthquakes along the coastal forearc of Chile‐Peru. To explain why elastic rebound in an offshore earthquake can cause widespread permanent deformation onshore, we propose a model in which the near‐surface material exhibits viscoelastic behavior, analogous to laboratory‐observed behavior of petroleum reservoir rocks. Because of near‐surface relaxation, interseismic deformation builds up stress only in the deeper crust. Elastic rebound of the deeper crust during an earthquake induces near‐surface tension to generate cracks. We numerically demonstrate the proposed mechanism using hypothetical and real megathrust earthquakes. The location of the zone of peak tension, assumed to be responsible for the crack generation, is controlled by downdip rupture termination. A rupture farther downdip or terminating more gradually causes the zone of peak tension to be farther landward and broader. The tension cracks thus may contain important information on megathrust rupture dynamics.
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