What roads are likely to be closed in an Alpine Fault quake?

3 MinutesBy NZ Trucking magazineMay 27, 2018

We should use lessons from Kaikoura to help us plan for future road closures caused by an earthquake on the Alpine Fault, according to a study in a special journal issue marking 300 years since the last Alpine Fault earthquake.

Both SH1 and SH70 were closed by landslides in the Kaikoura quake – blocking off Kaikoura and the surrounding communities and requiring those stranded there to be evacuated by air and sea. Using data about the slope steepness and how much the ground moved during the quake, the author predicts SH6 between Hokitika and Haast, SH73 near Arthur‘s Pass, and SH94 south of Milford Sound are all likely to be affected by landslides in an Alpine Fault earthquake – likely stranding many tourists.

The 2016 MW 7.8 Kaikoura earthquake involved complex rupture of multiple faults for > [greater than] 170 km, generating strong ground shaking throughout the upper South Island leading to widespread landslides. As a result of surface fault rupture and landslides, SH 1 and SH 70 were blocked, isolating Kaikoura and the surrounding communities, and necessitating evacuations by air and sea. In all these respects, the Kaikoura earthquake can be considered an analogue for a future Alpine Fault earthquake, providing lessons for the necessary emergency response.

Landslide blockages primarily occurred where surrounding slopes averaged > 17° and where peak ground acceleration was > 0.43 g, peak ground velocity was > 41 cm/s, or the modified Mercalli intensity was > 7.9. Using a potential future Alpine Fault scenario earthquake, this study identifies locations on other key state highway routes that have similar predictive variables that may, therefore, become blocked in a future earthquake.

This suggests that SH6 between Hokitika and Haast, SH73 near Arthur‘s Pass, and SH94 south of Milford Sound are all likely to be affected. This will necessitate the evacuation of large numbers of spatially distributed tourists as well as the resupply of isolated local populations. The possibility of bad weather along with a lack of sea ports south of Hokitika will likely make such activities challenging. Contingency planning based on experiences from the Kaikoura earthquake is therefore necessary and likely to prove invaluable following an Alpine Fault earthquake.