New Zealand Statistical Association 2024 Conference

Jessica Allen

University of Otago

Statistical modelling of slow and fast earthquakes in the Hikurangi Subduction Zone, New Zealand

This is joint work with Ting Wang, Mark Bebbington, Calum Chamberlain, Charles Williams, Andrea Perez Silva

The Hikurangi Subduction Zone (HSZ) is a large plate boundary system located beneath the North Island of Aotearoa that generates diverse and frequent activity, including mega thrust earthquakes. Improved catalogues of seismicity and slow slip events, developed using matched filter and wavelet analysis respectively, are paired with statistical methods to decipher the interactions between these behaviours and gain insights into the future of the Hikurangi region. Slow slip events are a kind of slow-motion earthquake, and have been associated with both large earthquakes and seismic swarms in the HSZ. Seismic swarms are spatially and temporally clustered sequences without typical mainshock-aftershock decay. Although the boundary between mainshock-aftershock and swarm activity is not clearly defined, swarms rely less on earthquake to earthquake triggering and arise from diverse underlying processes. In our analysis, relevant seismic sequences are first identified non-parametrically and classified into 2D spatial subregions using Gaussian mixture models. Within these subregions, the mutual information between seismicity and slow slip occurrence times provides evidence of precursory, co-occurring, and subsequent slow slip in relation to seismicity. A parametrisation of the mutually exciting Hawkes process is implemented to determine the strength and direction of the linear causal relationships between the two processes. We also use point processes to model event recurrence patterns across seismic sequences to distinguish mainshock-aftershocks from seismic swarms. The epidemic-type aftershock sequence model captures the triggering relationships of mainshock-aftershock activity, while swarm-like sequences are better described using renewal processes.