Characterization of Focal Mechanisms for Upper Crustal Distributed Seismicity in Aotearoa New Zealand

Abstract Applying distributed seismicity models for seismic hazard analysis requires postulating the styles of faulting and nodal planes for anticipated earthquakes. Here, we present a model describing focal mechanisms, or more specifically, strike, dip, and rake angles, for the ruptures of shallow (hypocentral depth ≤40 km) crustal earthquakes in Aotearoa New Zealand. This model is based on delineations of neotectonic domains and analysis of pre-existing datasets, including an active fault database, geological map-based fault datasets, the New Zealand Community Fault Model, and a regional moment tensor catalog. We demonstrate that the focal mechanism model is broadly consistent with the regional moment tensor catalog, with respect to spatial distributions of P and T axes and in terms of the Kagan angle. This characterization of focal mechanisms complements the distributed seismicity component of the New Zealand National Seismic Hazard Model 2022.