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The Rates of Large and Moderate Earthquakes in Aotearoa New Zealand

Description: 

For use in the Seismicity Rate Model (SRM) component of the 2022 New Zealand National Seismic Hazard Model, we estimate the total magnitude-frequency distribution (MFD) of earthquakes in the greater New Zealand region and along the Hikurangi–Kermadec and Puysegur subduction zones. The former is a key input into multiple components of the SRM in the onshore and near-shore regions, while the latter is a key input into models of earthquake rupture rates on the subduction zones.

Recent work (Christophersen et al., 2022) has greatly improved and homogenized the earthquake magnitudes in the New Zealand earthquake catalogue for use in the NZ NSHM 2022. Other parameters in the catalogue remain of mixed quality, however, in particular earthquake depths. Therefore, we develop an augmented New Zealand earthquake catalogue in which we import higher-quality depths and depth uncertainties, focal mechanisms, and some locations and magnitudes from several relocated and global catalogues. Next, we use event depths, focal mechanisms, 3D models of the Hikurangi and Puysegur subduction interfaces, and relative plate motion directions to classify earthquakes as upper-plate, interface or intraslab.

Using this augmented catalogue and adapting an approach used previously in California, we estimate the MFD of earthquakes in the near-shore region incorporating data back to 1843, balanced with the better data in the more recent part of the instrumental catalogue. This method estimates both the mean earthquake rate and its uncertainty, and we supplement it with an alternative estimate of the rate uncertainty that is based on the rate variability in the catalogue over a range of shorter timespans. We estimate the MFDs on the Hikurangi–Kermadec and Puysegur subduction zones using a simplified version of the method used in the near-shore region, with more recent data. Finally, we describe a globally based method to estimate the potential earthquake rate uncertainty on the Hikurangi–Kermadec subduction zone.

Session: Opportunities and Challenges in Source Modeling for Seismic Hazard Analysis [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Chris Rollins

Student Presenter: No

Invited Presentation: No

Authors