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

Abstract

The 2013 Cook Strait earthquake sequence began on 18 July 2013 with two foreshocks of Mw 5.7 and Mw 5.8 and culminated in the Mw 6.6 Cook Strait and Lake Grassmere events on 21 July and 16 August, respectively. Located ∼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.

Complex multifault rupture during the 2016 M w 7.8 Kaikōura earthquake, New Zealand

“…Aftershocks follow a broad NE-SW trend proximal to the Humps and Hundalee faults for ~80 km extending offshore near Kaik ura (Figure 1, S1). The aftershocks then step north, approximately following the Jordan Thrust and Kekerengu faults, with a large cluster of events occurring in the Cape Campbell and Lake Grassmere area (Figure 1), the site of a Mw 6.8 earthquake in 2013 (27). Regional moment tensors (28) for aftershocks show a mixture of reverse and strike slip mechanisms with the majority of events occurring in the upper 20 km ( Figure S1).…”

Quake clamps down on slow slip

“…The NIF is a Kalman filter‐based method that allows us to investigate in detail the timing and location of SSE slip‐rate changes after the Eketahuna earthquake. Prior to running the NIF, we correct the cGPS time series for small coseismic displacements observed at some nearby cGPS sites during the 20 January Eketahuna earthquake, as well as coseismic displacements from Hamling et al [] for a sequence of earthquakes in Cook Strait in June/July 2013.…”

Quantifying seismicity associated with slow slip events in the Hikurangi margin, New Zealand

“…Using InSAR (interferometric synthetic aperture radar),Hamling et al (2015) have shown potential movement along this fault during the 2004-2005 Manawatu SSE. We also note that the earthquakes in Upper Hutt 2004-2005, Masterton 2010 and the M L >5 earthquake further north along the Wellington fault during the Manawatu 2004-2005 SSE all have broadly similar, normal, CMT solutions.…”