Rapid Remeasure of Dense Civilian Networks As a Game‐Changer Tool for Surface Deformation Monitoring: the Case Study of the Mw 6.4 2020 Petrinja Earthquake, Croatia

The M-w 6.4 right-lateral Petrinja earthquake (2020, Croatia) is one of the largest continental earthquakes of central Europe for decades. The slip pattern of such events is usually difficult to retrieve with terrestrial geodesy due to limited monitoring means. This study takes advantage of a unique data set of dense measurements of coseismic displacement in the epicentral area, obtained by repeated measurements of benchmark networks designed for civilian purposes, and supplemented by far-field continuous GNSS measurements. Elastic modeling of these data shows two coseismic slip patches that extend over a 15 x 10 km rupture plane, locally reaching the surface, and that a right-lateral sub-parallel secondary fault in the central part of the rupture likely accommodated part of the coseismic deformation. This study demonstrates that rapid re-measurement of pre-existing civilian networks offers unique coseismic constrains in the near-field where InSAR or optical image correlation may decorrelate.