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An Analysis of the Fault Surface Ruptures from the Mw 7.8 Earthquake in New Zealand
About 12 hours after a Mw 7.8 earthquake struck New Zealand, the resulting deformation on the ground became evident. Based on field photos shared by the media and on social media channels, it is clear that fault surface ruptures had appeared in various locations on the northeastern coast of the South Island.
Along the coastal highway near Kaikoura, which is a two-hour drive north of Christchurch, surface ruptures close to the northeastern extension of the mapped Hundalee Fault are clearly visible, with an approximately 1-metre (m) vertical displacement.
South of Blenheim, near the town of Ward, photos released by Reuters suggest that the fault surface rupture obliquely offsets New Zealand’s State Highway One, with a dextral displacement that is likely larger than 2 m, and a vertical displacement that is less than 1 m. Based on the aerial photos taken of the mapped Kekerengu fault system in Kekerengu Valley, between Blenheim and Kaikoura, the dextral displacement along the surface rupture is likely to be over 4 m in length.
A Global Positioning System (GPS) station in Cape Campbell has found horizontal ground displacements measuring about 2.5 m during the Mw 7.8 main shock event, and surface uplifting of close to 1 m near the northeastern end of the fault rupture. From the maps provided by Dr Jianghui Geng from Wuhan University, the GPS data reveal a complicated ground deformation pattern that stretches throughout the entire length of the rupture.
Another station, located close to the earthquake’s epicentre, has found significant shortening in the rupture as compared to the one found in Cape Campbell. This suggests that the direction of the fault slip has changed from one that is oblique to an almost dextral slip, moving from southwest to northeast. A detailed analysis from New Zealand’s geodetic data will certainly provide critical information on this earthquake event.