Diverse slow slip behavior at the Hikurangi subduction margin, New Zealand

Abstract

The installation of a continuous GPS (cGPS) network in New Zealand since 2002 has enabled the discovery of 15 slow slip events at the Hikurangi subduction margin. Our analysis and interpretation of the cGPS data reveal a marked diversity in characteristics of slow slip events (SSEs) in the North Island, with durations varying from 6 days to 1.5 years, equivalent moment release between Mw 6.3–7.2, and recurrence intervals of repeating SSEs on the order of 2 years to more than 5 years. The duration and magnitude characteristics of Hikurangi SSEs appear to be related to the depth where they occur. The deepest, longest duration, and largest SSEs occur at the southern Hikurangi margin, near the downdip limit of deep (down to ∼40 km depth), strong interseismic coupling. The shallowest, shortest duration, smallest, and most frequent SSEs occur at the northern and central Hikurangi margin near the downdip limit of unusually shallow (<10–15 km depth) interseismic coupling. The direction of slip on the interface in the Hikurangi SSEs is consistent with slip partitioning at the Hikurangi subduction margin. We also show that moment accumulation rates on the interface for the time periods between SSEs are ∼40% higher than for the period of more than a decade averaging through the SSEs, indicating that SSEs compose a major portion of the overall moment release budget of the Hikurangi subduction interface.