Like many parts of New Zealand, the Wellington Region is subject to earthquakes and has many active faults which present a major earthquake hazard. A multidisciplinary team of specialists have collaborated to build a robust 3D subsurface model of the Wellington Region using Leapfrog Works’ dynamic 3D modelling solution.
Wellington, New Zealand not only holds significance as the capital city – it also houses important infrastructure such as New Zealand Parliament, Te Papa – New Zealand’s national museum and key transport routes between the North and South Islands. Like many parts of New Zealand, the Wellington region is subject to earthquakes and has many active faults which present a major earthquake hazard. Understanding the seismic risk of the capital requires an in depth understanding of the complex geology and structures that lie beneath. Only in this way can future engineering decisions be made that help limit impact from future earthquakes.
GNS Science: Te Pū Ao, University of Auckland and the Natural Hazards Research Platform have collaborated to map the subsurface of the Wellington Region and to create a 3D subsurface model using Leapfrog. The project has been ongoing for several years and aims to update the first 3D subsurface model of the Wellington Region from 2010 with the latest geological data and understanding. The model will be used to inform future engineering and building decisions.
Multiple disciplines are represented in the project including seismologists, engineering geologists, geophysicists and geologists. The project has benefited from advances in Leapfrog software and to-date there have been 22 model versions accruing some 81GB of data. The iterative nature of the project has been a key feature, requiring regular updating of the 3D subsurface model. The ability to readily share key model views with the multi-disciplinary team has also been an essential component to ensure fast, clear communication and interpretation.
Matthew Hill, of GNS Science, comments, “The Leapfrog 3D subsurface model really helped the multi-disciplinary team to communicate as it created an interactive environment, contributing to conversation and collaboration.”
A wealth of new data was incorporated to improve the 3D model of the basin subsurface and update maps of key geotechnical properties. This varied surface and subsurface data included new geophysical measurements, new Light Detection and Ranging (LiDAR) surveys and an updated borehole database. The project also benefitted from access to the New Zealand Geotechnical Database, (NZGD), a newly established national repository for new and existing geotechnical information. Leapfrog was able to readily incorporate all of these varied data types to produce a robust model with a high degree of corroboration from the varied data sources.
Using the dynamic updating feature in Leapfrog, the multi-disciplinary team was able to work with live borehole data.
“The team were able to effectively update and rerun and recalculate the whole of the model as the project progressed,” said Matthew.
Using ‘View’ Leapfrog’s web-based solution for viewing and interacting with Leapfrog models, all stakeholders were able to easily access updates to key model views. “Everyone can open the model on their own computer and review prior to meetings or discussions. This really helps speed up communication and understanding in a multi-disciplinary study like this,” continues Matthew.
Discovery of the Aotea Fault
A key milestone in the project was the discovery by Crown Research Institute, The National Institute of Water and Atmospheric Research, (NIWA), that the Aotea Fault, previously considered to be inactive, was actually an active fault.
“The identification of the new active fault by NIWA made a big difference. The discovery revealed that along with the Wellington Fault, the basin is bound by faults on both sides. Using Leapfrog we were able to easily add and activate the fault in the model, which was particularly useful as we didn’t have a lot of borehole data in some areas near the fault. But the borehole data we did have, and the geophysical data really correlated well with the newly modelled fault block.,” says Matthew.
With the newly improved 3D model, engineers and seismologists are able to assess and review the model and decide on a site class map that Council’s will refer to regarding engineering requirements. Having this up to date and vastly improved 3D geological model will help to guide robust engineering design practices that take into account site-specific ground shaking characteristics. Ultimately, the model will help Councils to plan and advise on building requirements to ensure that the risk of damage from future earthquakes is mitigated.
Seequent’s Civil and Environmental Product Manager, Pat McLarin, comments, “We’re pleased Leapfrog’s dynamic 3D modelling has been pivotal in this significant research project to bring together the combined efforts from a broad cross disciplinary team into a single robust 3D subsurface model. Leapfrog provides an unrivalled level of accuracy and efficiency in understanding ground conditions. As an organisation that’s been directly impacted by earthquakes in the past, it’s satisfying that our solutions are contributing to better understanding and mitigation of their impact on others in the future.”
You can learn more about the project by reading the full case study here.
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