InSAR imaging of displacement on flexural-slip faults triggered by the 2013 Mw 6.6 Lake Grassmere earthquake, central New Zealand

Interferometric Synthetic Aperture Radar (InSAR) data reveal surface slip on multiple faults triggered by the 2013 Mw 6.6 Lake Grassmere earthquake, New Zealand. Surface offsets of 1-2cm occurred on previously inferred flexural-slip faults located approximate to 4km from the epicenter. We document dip slip on at least three different northeast striking, northwest dipping, flexural-slip faults located in the western limb of a syncline. The along-strike extent of the triggered slip is 1-1.5km for each fault. Dislocation models suggest that triggered slip is confined to shallow depths (approximate to 800m). Coulomb stress analysis indicates that slip was not triggered by the static stress change of the main shock but was likely caused by dynamic shaking during the passage of seismic waves. Our finding also provides an important clue on how some slip on shallow flexural-slip faults takes place.