The proximity of the Greater Wellington Region (GWR) to numerous active faults poses a sizeable earthquake hazard that has implications for the whole of Aotearoa New Zealand. The 2022 National Seismic Hazard Model suggests multiple plausible, major earthquake scenarios that would have significant impacts for the region. Whilst seismic hazard in the GWR is relatively well-studied, the cascading hazards, particularly landslides, are less well understood. Despite the known impacts of earthquake-induced landslides (EQIL), and the acknowledgement of EQIL risk in existing seismic hazard analyses, the potential consequences of this cascading hazard have not been quantified at a high resolution in the GWR. This is especially important in the context of the 2015 Sendai Framework, where the need for multihazard approaches to disaster risk reduction has been emphasised. Furthermore, with the range of plausible earthquake scenarios in the GWR, traditional approaches to seismic hazard analysis are becoming progressively unsuitable to assess seismic impacts across multiple seismic events. Most seismic hazard and risk assessments for GWR to date have focussed on probabilistic estimates of hazard or a limited number of potential scenarios involving rupture of the Wellington Fault or the Hikurangi Subduction Zone. However, given the number of plausible earthquake scenarios that could affect GWR, understanding whether each scenario produces bespoke impacts or if consistent impacts are seen in multiple scenarios is critical for planning. Ensemble modelling utilises a range of plausible earthquake scenarios to assess the variability of seismic impacts for a given area, combining strengths of existing deterministic and probabilistic approaches and therefore presents a potential opportunity for advancing a holistic understanding of seismic risk in this region.

This study assesses the variability in EQIL hazard and resulting impacts in the GWR for a plausible earthquake scenario ensemble. It uses a statistical landslide model by applying fuzzy logic within GIS to determine landslide hazard for ten plausible earthquake scenarios across the GWR. The exposure of the road network to landsliding across the earthquake scenario ensemble is then estimated, to assess potential disruption to key routes and emergency water access. Importantly, this research explores how this exposure and disruption might vary between earthquake scenarios. The results show the criticality of multi-hazard, multi-scenario approaches for assessing seismic risk; although the extent and severity of EQIL hazard potential was variable across the ensemble, plausible EQIL impacts were present within the GWR across every modelled scenario. Numerous low-specificity impacts have been identified The proximity of the Greater Wellington Region (GWR) to numerous active faults poses a sizeable earthquake hazard that has implications for the whole of Aotearoa New Zealand. The 2022 National Seismic Hazard Model suggests multiple plausible, major earthquake scenarios that would have significant impacts for the region. Whilst seismic hazard in the GWR is relatively well-studied, the cascading hazards, particularly landslides, are less well understood. Despite the known impacts of earthquake-induced landslides (EQIL), and the acknowledgement of EQIL risk in existing seismic hazard analyses, the potential consequences of this cascading hazard have not been quantified at a high resolution in the GWR. This is especially important in the context of the 2015 Sendai Framework, where the need for multihazard approaches to disaster risk reduction has been emphasised. Furthermore, with the range of plausible earthquake scenarios in the GWR, traditional approaches to seismic hazard analysis are becoming progressively unsuitable to assess seismic impacts across multiple seismic events. Most seismic hazard and risk assessments for GWR to date have focussed on probabilistic estimates of hazard or a limited number of potential scenarios involving rupture of the Wellington Fault or the Hikurangi Subduction Zone. However, given the number of plausible earthquake scenarios that could affect GWR, understanding whether each scenario produces bespoke impacts or if consistent impacts are seen in multiple scenarios is critical for planning. Ensemble modelling utilises a range of plausible earthquake scenarios to assess the variability of seismic impacts for a given area, combining strengths of existing deterministic and probabilistic approaches and therefore presents a potential opportunity for advancing a holistic understanding of seismic risk in this region. This study assesses the variability in EQIL hazard and resulting impacts in the GWR for a plausible earthquake scenario ensemble. It uses a statistical landslide model by applying fuzzy logic within GIS to determine landslide hazard for ten plausible earthquake scenarios across the GWR. The exposure of the road network to landsliding across the earthquake scenario ensemble is then estimated, to assess potential disruption to key routes and emergency water access. Importantly, this research explores how this exposure and disruption might vary between earthquake scenarios. The results show the criticality of multi-hazard, multi-scenario approaches for assessing seismic risk; although the extent and severity of EQIL hazard potential was variable across the ensemble, plausible EQIL impacts were present within the GWR across every modelled scenario. Numerous low-specificity impacts have been identifiedThe proximity of the Greater Wellington Region (GWR) to numerous active faults poses a sizeable earthquake hazard that has implications for the whole of Aotearoa New Zealand. The 2022 National Seismic Hazard Model suggests multiple plausible, major earthquake scenarios that would have significant impacts for the region. Whilst seismic hazard in the GWR is relatively well-studied, the cascading hazards, particularly landslides, are less well understood. Despite the known impacts of earthquake-induced landslides (EQIL), and the acknowledgement of EQIL risk in existing seismic hazard analyses, the potential consequences of this cascading hazard have not been quantified at a high resolution in the GWR. This is especially important in the context of the 2015 Sendai Framework, where the need for multihazard approaches to disaster risk reduction has been emphasised. Furthermore, with the range of plausible earthquake scenarios in the GWR, traditional approaches to seismic hazard analysis are becoming progressively unsuitable to assess seismic impacts across multiple seismic events. Most seismic hazard and risk assessments for GWR to date have focussed on probabilistic estimates of hazard or a limited number of potential scenarios involving rupture of the Wellington Fault or the Hikurangi Subduction Zone. However, given the number of plausible earthquake scenarios that could affect GWR, understanding whether each scenario produces bespoke impacts or if consistent impacts are seen in multiple scenarios is critical for planning. Ensemble modelling utilises a range of plausible earthquake scenarios to assess the variability of seismic impacts for a given area, combining strengths of existing deterministic and probabilistic approaches and therefore presents a potential opportunity for advancing a holistic understanding of seismic risk in this region. This study assesses the variability in EQIL hazard and resulting impacts in the GWR for a plausible earthquake scenario ensemble. It uses a statistical landslide model by applying fuzzy logic within GIS to determine landslide hazard for ten plausible earthquake scenarios across the GWR. The exposure of the road network to landsliding across the earthquake scenario ensemble is then estimated, to assess potential disruption to key routes and emergency water access. Importantly, this research explores how this exposure and disruption might vary between earthquake scenarios. The results show the criticality of multi-hazard, multi-scenario approaches for assessing seismic risk; although the extent and severity of EQIL hazard potential was variable across the ensemble, plausible EQIL impacts were present within the GWR across every modelled scenario. Numerous low-specificity impacts have been identified across the GWR; as a result, some impacts can be prepared for even when the next major earthquake is unknown. For example, high exposure and subsequent disruption to State Highway 2 (Ngauranga to Petone) and the coastal route from Seaview to Eastbourne was observed across all 10 earthquake scenarios, with severe disruption to access routes for the emergency water station in Days Bay, in Lower Hutt, suggested in five of the 10 scenarios. Conversely, the location and extent of impacts to State Highway 1 and 58 varied across the selected ensemble, and severe disruption to emergency water stations in Huntleigh Park and Karori was limited to only scenarios on the Ohariu and Wellington Faults. The distinction between consistent and scenario-specific impacts is made to indicate the variability of these impacts across earthquake scenarios, and to highlight the level of uncertainty in the manifestation of impacts depending on the magnitude and location of fault rupture. What the scenario model ensemble has stressed is the extent to which some impacts occur, irrespective of which plausible, major earthquake is utilised in impact modelling. Understanding the specificity of coseismic impacts across the GWR provides a much-needed platform to assess the criticality of risk reduction across infrastructure systems, to ensure planning efforts will mitigate impacts for a range of plausible seismic events.