New research identifying activity on the Mangatangi Fault has prompted fresh concern about Auckland's earthquake preparedness and the risk faced by communities in the city's south.

Researchers have warned the fault, which runs near the Hunua Ranges, could potentially generate a magnitude 6.8 earthquake if it ruptured along its length.

Experts say the finding highlights how much remains unknown about the region's seismic history. For a city more often associated with volcanic risk than earthquakes, the research is a reminder that Auckland's emergency planning needs to cover more than one kind of natural hazard.

Local agencies are likely to face renewed pressure to update preparedness messaging and review the resilience of infrastructure in the city's south.

The key question will be whether this moment leads to a short-term reaction or a more durable change in how seismic risk is communicated.