The 2019 East Coast Slow Slip Event, New Zealand: Spatiotemporal Evolution and Associated Seismicity

Abstract

Slow slip events (SSEs) are interpreted as the transient quasi-static fault deformation in the deep transition zone from locked to freely slipping in many subduction zones. Using continuous Global Positioning System (cGPS) data collected in New Zealand, we estimate the spatiotemporal evolution model during the 2019 SSE and analyze the influence of subduction interface heterogeneity on seismicity during SSEs at the Hikurangi margin. The results reveal that the 2019 SSE extends from the northern (Gisborne) to the central (Hawke’s Bay) Hikurangi subduction interface and decays rapidly within approximately 3-4 weeks. It releases a total seismic moment of about 4.83 × 1019 N·m (Mw 6.8), with a significant slip in Gisborne and a secondary slip in Hawke’s Bay. The slip depths are similar, but peaks, durations, and rates differ slightly. By combining previous SSEs (2011-2019), diverse characteristics are concluded, i.e., shorter duration and more frequency in Gisborne and relatively longer duration and less frequency in Hawke’s Bay. The seismicity offshore and onshore indicates along-strike variations, which appear to be spatially correlated with the variations in topography, such as subduction seamounts. The heterogeneities on the subduction interface are related to the spatiotemporal distribution of SSEs and seismicity along the Hikurangi margin.