On the determination of coseismic deformation models to improve access to geodetic reference frame conventional epochs in low-density GNSS networks

For many practical applications, ranging from cadastre and engineering to scientific, GNSS locations must refer to a specific epoch in a known reference frame to establish a consistent spatial relationship between georeferenced features measured at different times. When an earthquake occurs, an effectively instantaneous coseismic offset in position is observed. This offset varies as a function of distance and direction from the earthquake's rupture zone and depends on its type and magnitude. When GNSS is used to measure the position of a point after an earthquake, the result includes the coseismic displacement suffered by that point and this displacement must be removed to provide coordinates in the conventional epoch. When post-event GNSS observations are far from continuous GNSS monitoring stations, their coseismic displacements are unknown and must be estimated using surrounding continuous GNSS stations. Interpolation of coseismic displacements, however, is difficult unless a sufficiently dense continuous GNSS network exists, especially in the near-field. We present a methodology for estimating coseismic displacements in areas with low-density continuous GNSS coverage by using geophysical models in a hybrid (dynamic-kinematic) mode. We do this using elastic deformation of a spherical earth to constrain the overall coseismic displacement field without imposing the usual geodynamic constraints on fault slip distribution. Application of this methodology to the 2010 Maule and 2015 Illapel, Chile, earthquakes provides coseismic estimates on survey GNSS stations with rms (95% confidence interval) residuals of similar to 3 cm for Maule, and similar to 2 cm for Illapel. We also tested our models using InSAR and found that the models correctly predict the near-field deformation.