Catalyst: Strategic – New Zealand – Japan Joint Research Programme 2024

Aotearoa and Japan have multiple volcanoes capable of producing widespread ashfall. In Japan, ash 4 cm thick reached Edo (now Tokyo) during the 1707 Hoei eruption of Mount Fuji, and in Aotearoa, approximately 10 cm of ash fell in Rotorua, Whakatane, and Tauranga during the ~1314 Kaharoa eruption from Okataina volcano. These events, if they were to occur again today, would cause substantial impacts in both urban and rural areas, affecting lifelines, transport, health, farming, manufacturing, and business. This project will form a coalition of researchers and stakeholders from Aotearoa and Japan to understand and mitigate the impacts of future widespread ashfalls. 

Traditional natural hazard risk assessment often takes a hazard-led approach, where a hazard is defined and the corresponding impacts are then assessed. However, the problem with this approach is that the hazard event that occurs is rarely the event that has been assessed, which makes identifying useful mitigation strategies difficult. We will flip the problem and use an impact-led approach where we will first define impact tolerability thresholds (e.g., duration of service outages) and then utilise ashfall simulations to identify the conditions where these thresholds would be exceeded. This will involve close engagement with stakeholders to establish an understanding of the tolerability of outages and disruption to services, and how these might vary between countries. We will consider ideal and mandated thresholds for service providers (water, electricity, transport, etc.) and service requirements for various sectors (emergency response, manufacturing, primary industry, etc.). 

Our new modelling approach and stakeholder involvement throughout the project will combine to enable Aotearoa and Japan to more effectively assess their current capacity to manage ashfall. The approach will allow mitigation strategies to be explored leading to safe evacuations, optimised response, and faster recovery. We will build a shared understanding of mitigation strategies across both countries, recognising our unique physical and cultural environments. Internally, each country will have better understanding and coordination of response and recovery.

A structural retrofitting system is proposed to enhance the resilience of buildings during seismic events, focusing on controlling relative lateral movement between two consecutive floors (i.e., drift), which can lead to significant damage in an earthquake. This research addresses the challenges faced by earthquake-prone countries, New Zealand and Japan, where many buildings were constructed before modern seismic standards were established. A tragic example is the Canterbury Earthquakes, where uncontrolled drift led to irreparable damage to numerous buildings. Thus, the seismic resiliency of these older buildings needs urgent improvements, commonly achieved by using concrete shear walls, masonry infills, and steel braces, which pose limitations from the design, installation, structural integrity, and environmental impact aspects. 

Our proposed solution is a modular infill system using Cross-Laminated Timber (CLT) panels in combination with Phase-transforming Cellular Materials (PXCM). This system offers a more sustainable and adaptable alternative to traditional methods of strengthening buildings. By utilising CLT, a sustainable engineered wood product manufactured by consolidating layers of timber orthogonal to each other, and PXCM, an advanced material that can absorb earthquake demands while remaining damage-free by changing the geometry of its internal structure, we aim to create a system that not only effectively controls drift but also reduces the time required to reoccupy buildings after earthquakes. 

Our research includes developing innovative PXCM connection systems between CLT panels and structural frames. These connections will allow energy dissipation while reducing damage, making the system more seismic resilient and cost-effective. Additionally, the modular nature of CLT panels, which can be manufactured off-site, will allow for easy installation and reconfiguration, reducing the construction time while offering versatile design. 

We aim to demonstrate the effectiveness of this system through experimental testing and numerical modelling, including large-scale earthquake simulations. Our findings will be used to develop design recommendations specifically for buildings in New Zealand and Japan. This innovative approach promises to offer a more sustainable, economical, and adaptable solution for protecting buildings from the devastating effects of earthquakes. 

The Hikurangi subduction zone is New Zealand’s largest source of earthquake and tsunami hazard. However, the lack of great (M8+) earthquakes in historical records means that key uncertainties remain regarding both the magnitude and location of future earthquakes, and the size and impact of resulting tsunami. A novel approach to reduce these uncertainties is through comparison with Japan, whose two subduction zones provide the closest structural and tectonic equivalents to the Hikurangi subduction zone, but are distinguished by extensive geophysical datasets, world-leading earthquake monitoring networks, and the recent occurrence of giant earthquakes (e.g. 2011 M9 Tohoku-oki). 

To date, detailed comparisons have been limited by major differences in the resolution of geophysical images (akin to CAT scans) required to constrain subduction zone structure. This project will unlock comparative subduction zone research by partnering with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) to extend new high-resolution seismic imaging techniques recently pioneered by our team at New Zealand’s Hikurangi Margin to NE Japan and the source of the 2011 M9 Tohoku-oki earthquake. We will collect new data, using the JAMSTEC research vessel R/V Kamei, to conduct the first dedicated seismic survey into the largest seafloor subduction zone monitoring cable (S-Net) on Earth. These data will enable our team to produce directly analogous models of subduction fault structure and the distribution of rock properties for the Hikurangi Margin and Japan Trench. 

These models will underpin the use of advanced earthquake rupture simulations to investigate how subduction zone structure impacts earthquake and tsunami processes. These simulations will be tuned to test two key hypotheses. The first concerns the 2011 Tohoku earthquake, where abrupt changes in the distribution and properties of rigid crustal rocks above the fault are thought to have contributed to more than 60 m of fault slip, generating a tsunami that affected over 2,000 km of coastline with waves up to 40 m high. Prior research by our team has suggested that similar boundaries and distributions of crustal rocks may exist along New Zealand’s Hikurangi Margin. The second hypothesis will test how these structures may impact the likelihood of a similar high-slip, trench-breaching rupture in New Zealand. 

This project will provide the high-resolution, regional constraints on subduction fault structure and properties that are necessary for both countries to improve the precision of subduction zone monitoring and employ next-generation methods of simulating earthquake ruptures, ground shaking, and tsunami generation.