ALBERT

Description: Macroseismic intensities play a key role in the engineering, seismological, and loss modeling communities. However, at present, there is an increasing demand for instrumental data-based loss estimations that require statistical relationships between intensities and strong-motion data. In New Zealand, there was an urgent need to update the ground motion to intensity conversion equation (GMICE) from 2007, developed prior to a large number of recent earthquakes including the 2010–2011 Canterbury and 2016 Kaikōura earthquake sequences. Two main factors now provide us with the opportunity to update New Zealand’s GMICE: (1) recent publication of New Zealand’s Strong-Motion Database, corresponding to 276 New Zealand earthquakes with magnitudes 3.5–7.8 and 4–185 km depths; and (2) recent generation of a community intensity database from GeoNet’s “Felt Classic” (2004–2016) and “Felt Detailed” (2016–2019) questionnaires, corresponding to around 930,000 individual reports. Ground-motion data types analyzed are peak ground velocity (PGV) and peak ground acceleration (PGA). The intensity database contains 67,572 felt reports from 917 earthquakes, with magnitudes 3.5–8.1, and 1797 recordings from 247 strong-motion stations (SMSs), with hypocentral distances of 5–345 km. Different regression analyses were tested, and the bilinear regression of binned mean strong-motion recordings for 0.5 modified Mercalli intensity bins was selected as the most appropriate. Total least squares regression was chosen for reversibility in the conversions. PGV provided the best-fitting results, with lower standard deviations. The influence of hypocentral distance, earthquake magnitude, and the site effects of local geology, represented by the mean shear-wave velocity in the first 30 m depth, on the residuals was also explored. A regional correction factor for New Zealand, suitable for adjustment of global relationships, has also been estimated.

Description: The corrected 2010 New Zealand National Seismic Hazard Model has been adapted for use in the Global Earthquake Model’s OpenQuake engine through an extensive benchmarking exercise with GNS Science’s legacy Fortran code. Resolution of differences between the legacy code and OpenQuake result in hazard curve output comparisons with discrepancies of less than 3% nationally and remaining discrepancies highlight challenges faced when moving away from in-house legacy code. OpenQuake’s multiple and varied computation options for both hazard and risk and OpenQuake’s consistent, software-friendly output formats allow for exploration and development of innovative approaches to future seismic hazard and risk modeling in New Zealand. The end-to-end seismic hazard-to-risk capabilities already enabled by the inclusion of New Zealand seismic hazard, vulnerability, and building exposure models in OpenQuake have already had significant impact on post-disaster response to the 2016 Kaikōura earthquake.