A continuous map of near-surface S-wave attenuation in New Zealand

Quantifying the near-surface attenuation of seismic waves at a given location can be important for seismic hazard analysis of high-frequency ground motion. This study calculates the site attenuation parameter, kappa(0), at 41 seismograph locations in New Zealand. Combined with results of a previous study, a total of 46 kappa(0) values are available across New Zealand. The results compare well with previous t* studies, revealing high attenuation in the volcanic arc and forearc ranges, and low attenuation in the South Island. However, for site-specific seismic hazard analyses, there is a need to calculate kappa(0) at locations away from a seismograph location. For these situations, it is common to infer kappa(0) from weak correlations with the shear wave velocity in the top 30 m, V-S30, or to adopt an indicative regional value. This study attempts to improve on this practice. Geostatistical models of the station-specific kappa(0) data are developed, and continuous maps are derived using ordinary kriging. The obtained kappa(0) maps can provide a median kappa(0) and its uncertainty for any location in New Zealand, which may be useful for future site-specific seismic hazard analyses.