Seismological investigation of Mw=7.3 Karmedec Islands (New Zealand) earthquake occurred on June 15, 2019

An Mw=7.3 earthquake occurred on June 15, 2019 in New Zealand, Kermadec Islands (30.644° S, 178.100° W, 46 km depth), in correspondence with the Tonga-Kermadec subduction zone, and was characterized by a tectonic setting of shallow reverse faulting.We investigated the preparatory phase from a seismological point of view, focusing on the analysis of seismic data in the period between January 1, 2018 and June 14, 2019 in an area limited by the Dobrovolsky strain radius. Specifically, the data from the global United States Geological Survey (USGS) and the national New Zealand (GEONet) earthquake catalogues are used in this study.To characterize the seismicity trend in terms of magnitude distribution variations and strain release with time, we made a two-step analysis. The first one was to calculate the magnitude of completeness (Mc), which is an important parameter when estimating b-values (Wiemer and Wyss, B. Seism. Soc. Am., 2000). After this preliminary step, we observed that the seismicity accelerated during the preparation phase of the earthquake through the Revised Accelerated Moment Release (R-AMR) method (De Santis et al., Tectonophysics, 2015).Finally, we found that the seismological research of the preparation phase of this earthquake helped to understand, together with other observations from ground and satellite, the so-called Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) phenomena prior to the mainshock.