In this paper, we perform hybrid broadband (0-10 Hz) ground motion simulations for the ten most significant events (Mw 4.7-7.1) in the 2010-2011 Canterbury earthquake sequence. Taking advantage of having repeated recordings at same stations, we validate our simulations using both recordings and an empirically-developed ground motion prediction equation (GMPE). The simulation clearly captures the sedimentary basin amplification and the rupture directivity effects. Quantitative comparisons of the simulations with both recordings and the GMPE, as well as analyses of the total residuals (indicating model bias) show that simulations perform better than the empirical GMPE, especially for long period. To scrutinize the ground motion variability, we partitioned the total residuals into different components. The total residual appears to be unbiased, and the use of a 3D velocity structure reduces the long period systematic bias particularly for stations located close to the Banks Peninsula volcanic area.
The Resilient Shorelines study at University of Canterbury (UC) is using the Avon Heathcote Estuary Ihutai to investigate ecosystem-based approaches to conservation planning and adaptation in response to environmental change. In particular, the study is using a novel opportunity to understand effects of the Canterbury earthquakes that may be similar to impacts of sea level rise. These result from topographic and bathymetry changes in and around the estuary and associated waterways (Beaven et al., 2012; Cochran et al., 2014) that have driven changes in hydrodynamics (Measures et al., 2011). Therefore the wider context for the work reported here is to develop methodologies for modelling the impacts of sea level rise on estuaries and coastal river mouths using the Avon-Heathcote Estuary/Ihutai as a case study. Initial objectives have included establishing the magnitude of earthquake-induced changes. Subsequent steps will include establishing the relationships between strong physical drivers such as water levels and salinity, and the spatial pattern of estuarine ecosystems. There is particular focus on understanding salinity changes in the upper estuarine ecosystem in the vicinity of the freshwater-saltwater interface. In these areas, species, habitats and ecosystems that are adapted to brackish conditions are expected to migrate in response to the inland penetration of salt water under sea level rise. An example is the location of īnanga spawning habitat that is associated with the inland extent of salt water intrusion on spring tides (Taylor, 2002). It is expected to be strongly affected by sea level rise. To facilitate the development of ecosystem-based scenario models for sea level rise, a salinity model with resolution at ecological meaningful scales was required. An existing fine scale hydrodynamic model was available using Delft3D software (Deltares, 2012) that had been developed for ECan and MBIE following the earthquakes (Measures & Bind, 2013). However, it had not been calibrated for salinity. A collaborative project was designed between UC and NIWA to calibrate the model and develop a scenario modelling approach for sea level rise at a level of resolution sufficient for understanding sea level rise impacts on īnanga (whitebait) spawning habitat. The project was allocated funding from Brian Mason Scientific and Technical Trust and commenced in late 2015. The purpose of this report is to provide a description of the model development process and an illustration of model outputs from an initial set of modelled scenarios for sea level rise.
