Amphibious Coastal Mapping Post-Earthquake in Kaikoura, NZ

The Strongest Earthquake in 150 years

Kaikoura region faultlines

Northeastern region of South Island, New Zealand (Canterbury). Faultlines shown in red lines and earthquakes (magnitude in yellow and red circles).

On 14 November, 2016 a powerful M7.8 earthquake shook North Canterbury, New Zealand. It was the strongest quake in over 150 years and is one of the most complex earthquakes ever recorded with modern instruments.

The rupture lasted nearly 2 minutes in total causing surface faults extensive displacement, horizontally up to 12 metres and vertically by up to 6 metres.

Since the quake, much of the land ruptures have been mapped and measured, however information was lacking in the offshore areas where the faults transverse the coast and go along the seabed, particularly around Kaikōura, NZ.

A New Survey Was Required

Land Information New Zealand (LINZ), funded a hydrographic mapping project in the nearshore waters surrounding Kaikoura peninsula to re-map 35,000 Hectares of seafloor.

Kongsberg 2040c dual head multibeam sensors

Kongsberg 2040c dual head multibeam sensors.

iXblue Pty Ltd was contracted to conduct hydrographic charting of the area, including marine protected areas designated for production of additional science­ bi-products.

From November 2017 to February 2018, these areas were sonified using high-resolution multibeam technology.

We also

  • performed backscatter analysis and laser scanning
  • acquired sediment samples
  • used drone-based photogrammetry to map the coast in specific sites.

Our goal was to make our maps used for more than just charting.

benefits-chart

How we mapped habitats

Eight subareas within the hydrographic survey area were investigated to produce scientific by-products in the form of habitat maps.

Acoustic backscatter intensity was used to identify the seafloor substrate; whether it is hard rock or soft mud, coarse or fine grained etc.  Various objects through the water column can also scatter the emitted sound pulse from the MBES, and this specific acoustic backscatter echo was recorded and analysed.

Examples of water column features included kelp beds, biomass accumulations (e.g. fish), and plumes from freshwater seeps.

By combining these datasets, the information becomes extremely useful for:

  • Hydro and land surveyors
  • Fisheries
  • Government agencies
  • Tourism operators
  • Scientists/scholars

Seafloor Examples in This Region

Rocky reefs

Rocky reefs provide valuable habitat to globally unique assemblages of fish, kelp and invertebrate communities.  Protection of these delicate environments requires understanding the effects of fisheries and geohazard impacts.  Management of reserves must include detailed mapping to monitor changes over time.

Backscatter draped on bathymetry over rocky reefs.

Backscatter draped on bathymetry over rocky reefs.

Submarine  canyons

Submarine canyons are the conduit connecting the shallow shelf environments with the nutrient-rich deep sea.  They also funnel sediments away from the shallows to deeper depths.  Canyon morphology and evolution is closely tied to the tectonic regime.

The 7.8 earthquake impacted the canyon heads causing shoreward regression from extensive slope failures, especially proximal to oblique faults.

Mid-water column data shows a positive association with canyon head from higher nutrient exchange.

Backscatter draped on bathymetry over submarine canyons.

Bathymetric maps (red shallow- purple deep).

Faults

Due to the dynamic tectonic environment in the Canterbury region, extensive faulting occurs both onshore and offshore.  Many of the faults onshore have been mapped, and rupture extents measured precisely.

However, there are still many undocumented offshore fault lines.  Understanding the location and fault geometry will assist in geohazard management and scientific advancements.

While it remains difficult to predict earthquake activity and resulting damage, knowing potential rupture zones could provide insight for infrastructure and safety planning.

Bathymetric maps (red shallow- purple deep)

Bathymetric maps (red shallow- purple deep) with interpretations (middle).

Backscatter draped on bathymetry.

See The Full Kaikoura Mapping Story

Like to see more?  Further details of this extensive project and an informative interactive, online map is available here:  KAIKOURA SEAFLOOR MAPPING

Elizabeth Johnstone

Dr. Elizabeth Johnstone is a marine geologist specializing in bathymetric surveying and sediment dynamics. She has over 15 years of experience using geophysical tools to conduct seafloor mapping around the world. She develops novel approaches to produce four-dimensional data products for integration into marine geological studies.

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