Crustal deformation and stress transfer during a propagating earthquake sequence: The 2013 Cook Strait sequence, central New Zealand

The 2013 Cook Strait earthquake sequence began on 18 July 2013 with two foreshocks of M-w 5.7 and M-w 5.8 and culminated in the M-w 6.6 Cook Strait and Lake Grassmere events on 21 July and 16 August, respectively. Located similar to 50 km south of New Zealand's capital, Wellington, the earthquakes generated the most significant ground shaking in the Wellington and Marlborough regions in recent decades. During the first event, located under Cook Strait, continuously recording GPS instruments across central New Zealand recorded up to 5 cm of horizontal displacement. Modeling suggests that the rupture was 25 km long with up to 90 cm of dextral strike slip. The second event, located 20 km to the southwest, caused displacements of up to 25 cm at GPS sites located around the Clifford bay area. In addition, two interferograms from RADARSAT-2 and TerraSAR-X showed up to 30 cm of line-of-sight displacement in the vicinity of Lake Grassmere. Modeling indicates predominantly dextral strike slip of up to 2.1 m. Coulomb Stress changes induced by the earlier foreshocks suggest that the Cook Strait event was triggered by the preceding events and that the Lake Grassmere event was subsequently triggered by the Cook Strait earthquake.