Surveying After an Earthquake: Assessing the Damage
2 minute read
At two minutes after midnight on November 14, 2016, a shift in the seabed sent a 7.8 magnitude earthquake shuddering through New Zealand’s South Island. When the quake ended, about two minutes after it began, the main state highway running through the island, on which the town of Kaikoura sits, was impassable in both directions. Kaikoura and the other coastal communities, roads and marinas were heavily damaged.
The Trimble Solution for Eliot Sinclair
- R8 GNSS Receiver
- SX10 Total Station
- Trimble Business Center
The dramatic uplift in the seabed left Kaikoura’s critical South Bay marina significantly altered. Boats, vital to the fishing and tourism industries, were suddenly unable to navigate during low tides––the marina water level was too low. To solve the problem, officials in Kaikoura needed a plan. So they contacted Eliot Sinclair, a premiere surveying, engineering, and planning company based in Christchurch, and asked the firm to conduct a survey of the South Bay marina area.
This would be no run-of-the-mill project. For one thing, just reaching the site was difficult, post-earthquake. For another, the crew was at the mercy of the tidal schedule. There was also the sheer complexity of having to acquire data on both land and sea. The Eliot Sinclair team assembled a powerful package of Trimble data collection and processing tools, and made their way to the worksite. Once there, they set up a tide gauge and tide pole and established a new benchmark for the chart data.
Then the technicians deployed two vessels––one a local fishing boat, the other a small Orion RIB the survey team brought with it from Christchurch––equipped with Single Beam Echo Sounders (SBES), to survey the sea bottom. The Trimble technology proved invaluable, particularly on a job where space was limited and the need for complete confidence in the data was high.
The Eliot field team used Trimble R8 GNSS receivers to reestablish control and the SX10 to perform a high-speed scan of the exposed rocks at low tide. This eliminated the need to manually measure points and provided richer data than that collected via single topo points on each rock outcrop. The SBES data, which had been measured over the same positions at high tide, provided redundancy that could be used for comparisons. Eliot also put a drone in the air over the site, and then combined the information it captured with all of the collected sensor data. The result was a real-world view of the marina and surrounding area––a highly precise picture of the damage caused by the quake.
The firm’s fast response, highly accurate data collection, and follow-up work to monitor progress were credited with helping local authorities effectively plan their repair work. The marina was able to reopen relatively quickly, which restored vital industry to the quake-damaged island.