Nowcasting-Based Earthquake Hazard Estimation at Major Cities in New Zealand

Large earthquakes, accompanied by many smaller ones in between, frequently strike New Zealand and adjoining areas. This study implements the earthquake nowcasting method and presents the results in terms of earthquake potential score (EPS) at 15 major population centers in New Zealand. Based on seismicity data, the EPS incorporates ensemble seismicity statistics in a discrete natural time domain to estimate the current level of seismic cycle progress on a 0–100% scale of extremity. Natural times mark the evolution of the process in terms of small interevent counts between consecutive large earthquakes in a defined area. Statistical inference from exponential, gamma, Weibull and exponentiated exponential distributions indicates natural time Weibull statistics in the study area. With the derived EPS corresponding to M ≥ 6 events, the following ranking of cities is observed, in decreasing order: Palmerston North (97%), Auckland (96%), Lower Hutt (95%), Porirua (95%), Wellington (95%), Nelson (94%), Hibiscus Coast (93%), Christchurch (92%), Invercargill (91%), Napier (87%), Rotorua (84%), Tauranga (82%), Dunedin (81%), Hamilton (77%) and Gisborne (6%). These nowcast scores are largely stable against some variations in the threshold magnitude, catalog time period and city region. Results of the contemporary earthquake hazard serve a variety of end-user applications in New Zealand.