Subduction zones exhibit variable degrees of interseismic coupling as resolved by inversions of geodetic data and analyses of seismic energy release. The degree to which a plate boundary fault is coupled can have profound effects on its seismogenic behaviour. Here we use GPS measurements to estimate co- and post-seismic deformation from the 2012 August 27, Mw7.3 megathrust earthquake offshore El Salvador, which was a tsunami earthquake. Inversions of estimated coseismic displacements are in agreement with published seismically derived source models, which indicate shallow (<20 km depth) rupture of the plate interface. Measured post-seismic deformation in the first year following the earthquake exceeds the coseismic deformation. Our analysis indicates that the post-seismic deformation is dominated by afterslip, as opposed to viscous relaxation, and we estimate a post-seismic moment release one to eight times greater than the coseismic moment during the first 500 d, depending on the relative location of coseismic versus post-seismic slip on the plate interface. We suggest that the excessive post-seismic motion is characteristic for the El Salvador-Nicaragua segment of the Central American margin and may be a characteristic of margins hosting tsunami earthquakes.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology