  A megathrust subduction earthquake (Mw7.8) struck the coast of Ecuador on
April 16th, 2016 at 23h58 UTC. This earthquake is one of the best-recorded
megathrust events up to date. Besides the mainshock, two large aftershocks have
been recorded on May 18th, 2016, at 7h57 (Mw 6.7) and 16h46 (Mw6.9). These data
make a significant contribution for understanding the attenuation of ground
motions in Ecuador. Peak ground accelerations and spectral accelerations are
compared with four ground-motion prediction equations developed for interface
earthquakes, the global Abrahamson et al. (2016) model, the Japanese equations
Zhao et al. (2006) and Ghofrani and Atkinson (2014), and one Chilean equation
Montalva et al. (2016). The four tested GMPEs are providing rather close
predictions for the mainshock at distances up to 200km. However, our results
show that high-frequency attenuation is greater for backarc sites, thus
Zetal2016 and Metal2016, which are not taking into account this difference, are
not considered further. Residual analyses show that G&A14 and Aetal2016 are
well predicting the attenuation of ground motions for the mainshock.
Comparisons of aftershock observations with Aetal2016 predictions indicate that
the GMPE provide reasonable fit to the attenuation rates observed. The event
terms of the Mw6.7 and Mw6.9 events are positive but within the expected
scatter from worldwide similar earthquakes. The intra-event standard deviations
are higher than the intraevent variability of the model, which is partly
related to the poorly constrained VS30 proxys.
