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TheNew Zealand National Seismic Hazard Model (NSHM) was recently overhauled and revised in a three-year international effort. Of the many inputs into the NSHM, three of the most important ones are the total magnitude-frequency distribution (MFD) of earthquakes in the near-shore upper-plate region (e.g. the 2010-16 Canterbury and 2016 Kaikoura sequences), the MFD on the Hikurangi-Kermadec subduction zone, and the MFD on the Puysegur subduction zone (e.g. the 2009 Dusky Sound earthquake). To constrain these MFDs, we need good earthquake magnitudes, good event depths, and focal mechanisms (the latter two in order to distinguish whether earthquakes in the subduction regions are upper-plate, interface or intraslab). Recent work (Christophersen et al., 2022) has greatly improved the earthquake magnitudes in the New Zealand catalogue. Starting from their catalogue, we import higher-quality event depths, focal mechanisms, and locations and magnitudes from several relocated and global catalogues. Next, we use event depths, focal mechanisms, 3D models of the Hikurangi and Puysegur subduction interfaces, and relative plate motion directions to classify earthquakes as upper-plate, interface or intraslab. Then using this integrated catalogue, we estimate the MFD of earthquakes in the upper-plate region incorporating data back to 1843, balanced with the better data in the more recent catalogue. We estimate the MFDs on the Hikurangi–Kermadec and Puysegur subduction zones using a simplified approach with more recent data. Here, we will describe ongoing work in this area, including incorporating new earthquake data and describing earthquake clustering and rate uncertainty in less model-driven ways., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The “Every Earthquake a Precursor According to Scale” (EEPAS) model provides the medium-term component of public earthquake forecasts in New Zealand (NZ). EEPAS employs the “precursory scale increase” (Ψ-) phenomenon to forecast future earthquake occurrence rates with time-horizons up to a few decades. Ψ is the rate and magnitude increase of minor earthquakes preceding major earthquakes. Three associated predictive-scaling relations link mainshock magnitude , precursor time and precursory area .Studies of Ψ in synthetic catalogues showed that the expected is inversely proportional to an overall reduction of fault slip rates. The slip-strain rate connection therefore motivates us to enhance EEPAS forecasts by incorporating strain-rate. We allow the time distribution in EEPAS to depend on the strain-rate and introduce an additional parameter to quantify this dependence. Optimising the new parameter for the New Zealand catalogue confirms an inverse proportionality between the local strain-rate and the local precursor time. The information gain over the original EEPAS model is small because few target earthquakes occur where the strain-rate is low. The forecast should be compensated for incompleteness of precursory earthquake contributions due to the limited lead-time from the start of the catalogue to the occurrence of target earthquakes. The incompleteness is especially severe for low strain-rate areas where is longer. Further incompleteness can result from the precursory area for some target earthquakes extending outside the region covered by the catalogue. Such considerations should improve forecasting for low strain-rate areas., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

This is an electronic supplement toA time-dependent seismic hazard model following the Kaikōura M7.8 earthquake. It was writtenby the same authors and published in the New Zealand Journal of Geology and Geophysics

The MW 7.8 14 November 2016 Kaikoura earthquake generated more than 10000 landslides over a total area of about 10000 km2, with the majority concentrated in a smaller area of about 3600 km2. The largest landslide triggered by the earthquake had an approximate volume of 20 (±2) M m3, with a runout distance of about 2.7 km, forming a dam on the Hapuku River. In this paper, we present version 1.0 of the landslide inventory we have created for this event. We use the inventory presented in this paper to identify and discuss some of the controls on the spatial distribution of landslides triggered by the Kaikoura earthquake. Our main findings are (1) the number of medium to large landslides (source area ≥10000 m2) triggered by the Kaikoura earthquake is smaller than for similar sized landslides triggered by similar magnitude earthquakes in New Zealand; (2) seven of the largest eight landslides (from 5 to 20 x 106 m3) occurred on faults that ruptured to the surface during the earthquake; (3) the average landslide density within 200 m of a mapped surface fault rupture is three times that at a distance of 2500 m or more from a mapped surface fault rupture ; (4) the “distance to fault” predictor variable, when used as a proxy for ground-motion intensity, and when combined with slope angle, geology and elevation variables, has more power in predicting landslide probability than the modelled peak ground acceleration or peak ground velocity; and (5) for the same slope angles, the coastal slopes have landslide point densities that are an order of magnitude greater than those in similar materials on the inland slopes, but their source areas are significantly smaller.