Seismic sensor network trial

24 July 2020

A close network of ground-shaking earthquake sensors that provides instant effects information after an earthquake is being installed for a trial in central Wellington.

The sensors will enable Wellington City Council – and subscribed business operators and building owners - to rapidly assess the condition of buildings and infrastructure after a shake throughout the city.

The network is being installed as part of an agreement between the City Council and Canterbury Seismic Instruments (CSI). CSI is the developer of the network, called Sentinel, which is an earthquake response service that delivers real-time earthquake building status updates to cities and building owners, occupiers and property managers.

Mayor Andy Foster says Sentinel will potentially present a number of significant advantages for the city as a whole following any sizeable earthquake – notably that the ground-shaking data will help emergency managers make quick decisions about which City Council buildings are safe for occupancy – and otherwise.

“This information can also, for example, allow a civil defence controller to make quick calls on which parts of the city might have to be ‘red zoned’ and which parts are still safe for use. It’s not hard to see how essential such data and informed decision-making can be in terms of public safety but also for the economic wellbeing of the city and region.”

Sentinel expansion is an ongoing investment for CSI in Wellington. CSI is providing access to the Sentinel service to the City Council for city-wide emergency management, along with specific information for Council buildings. Other building owners and tenants can also subscribe to Sentinel through CSI.

The Sentinel sensor network in Wellington will be at least 100 sensors, mainly installed in City Council traffic-light control cabinets at city intersections. The intention is that the sensors be no more than 200 metres apart.

The partnership between The Council and CSI involves free exchange of information from the network for City Council use in return for access to infrastructure to enable the installation of the system.

Dr Hamish Avery, the CTO and Government Relations Manager at CSI, says a dense grid is necessary to ensure accurate measurement of the shaking at every point due to the big differences in ground and soil conditions and subsurface structures in central Wellington.

“Over several hundred metres you can go from solid rock to reclaimed land to old marshy areas and stream beds in parts of the CBD. This means the shaking will vary greatly over small distances and helps to explain why some Wellington buildings were badly damaged in the 2016 Kaikoura quake, and had to be demolished, while others nearby were undamaged.”

Sentinel works by creating a range of ground shaking ‘heat maps’ from the dense sensor data for each earthquake in a range of different formats, from shaking relative to the Building Code to how much the ground has moved to the Mercalli Intensity scale. This information can be sent to different user groups within the City Council within two minutes of an earthquake and is converted to formats relevant to the various Council teams, such as emergency, water, and traffic management.

For city-wide emergency management, Sentinel allows the City Council to immediately observe which areas have exceeded Building Code thresholds. It can then decide which areas or classes of building need to be cordoned and submitted to closer inspection, and where to send the first-response teams. The ‘heat maps’ show probable damage to underground services such as power, water, and telecommunications.

At an individual building level, the shaking beneath a building is compared to its known strength and a damage estimate is made. For example if the shaking is at 120% of Code and the building is at 60% of Code strength the building should be closed and inspected, whereas if the shaking is 10% of Code and the building is new, it can remain operational, The Council will use this information to better respond to earthquakes for its own buildings and this information is also available as a service to commercial clients.

Sentinel will help the City Council improve safety and resilience by enabling quick, clear decisions on building occupancy that relates to the local shaking rather than estimates of damage based on the earthquake epicentre. It also informs detailed engineering inspections when needed and helps processing of insurance claims, whether for business interruption or repair or replacement.

Mercalli Intensity maps are freely available to the public through the Sentinel app and website. The Sentinel app lets people flag the locations of friends and family and be automatically informed of the shaking at these locations. This helps every person answer the most pressing questions in the aftermath of a quake: What should I do? What was the shaking like for my partner or parents? At my kids’ school? Where do I go first?

The information is delivered to users via text, email, website or via a smartphone app.

Sentinel has installations spanning New Zealand and is provided to a number of users ranging from hospitals, fire stations and airports, along with many commercial tenants, building owners and portfolio managers. The first sensors were installed in Christchurch in late 2018 along with Waimakariri District Council in early 2019. A network is also operating in Hutt City. With the inclusion of Wellington City, Sentinel marks an important step in providing complete coverage of the highest-risk population areas in the country. The Wellington Sentinel sensor installation has already begun, and completion is expected in September.