17:15 〜 18:45
[SSS08-P08] Fluid involvement in seismicity and slow slip events at New Zealand’s northern and central Hikurangi subduction zone
The Hikurangi subduction zone is located at the south end of the > 3000 km-long Tonga-Kermadec-Hikurangi subduction system, where the Pacific plate subducts westward under the Australian plate beneath the North Island of New Zealand. Previous work has identified that slow slip events (SSEs) along the plate boundary are sometimes accompanied with seismic swarms and that the two phenomena may be related by fluid movement. We systematically evaluate temporal relationships between earthquakes and SSEs in the northern and central Hikurangi margins to better understand their relationship and constrain causative phenomena.
We classify earthquakes close to the Hikurangi subduction interface into six types according to their hypocenters, focal mechanisms, and waveform similarity. Earthquakes in the upper plate and along the plate boundary are clustered, and earthquakes in the lower plate are homogeneously distributed. We detect SSE signals using daily GNSS positions for individual stations and evaluate temporal relationships between the earthquakes and the SSE signals.
In the northern Hikurangi margin, earthquakes in the lower plate are activated before SSEs, earthquakes on the subduction interface are activated dominantly during SSEs, and earthquakes in the upper plate are dominantly activated after SSEs. This upward migration of activations, and characteristic within-swarm migration patterns is consistent with fluid movement triggering these earthquakes. In the central Hikurangi margin, the activation patterns are different from the northern Hikurangi margin, suggesting that another triggering mechanism is active. We suggest that SSE-induced stress loading is a plausible mechanism of earthquake-triggering at the Southern Hikurangi margin. The regional difference we infer in earthquake-triggering mechanisms between the northern and central Hikurangi margins is consistent with other geological and geophysical features of fluid movement.
We classify earthquakes close to the Hikurangi subduction interface into six types according to their hypocenters, focal mechanisms, and waveform similarity. Earthquakes in the upper plate and along the plate boundary are clustered, and earthquakes in the lower plate are homogeneously distributed. We detect SSE signals using daily GNSS positions for individual stations and evaluate temporal relationships between the earthquakes and the SSE signals.
In the northern Hikurangi margin, earthquakes in the lower plate are activated before SSEs, earthquakes on the subduction interface are activated dominantly during SSEs, and earthquakes in the upper plate are dominantly activated after SSEs. This upward migration of activations, and characteristic within-swarm migration patterns is consistent with fluid movement triggering these earthquakes. In the central Hikurangi margin, the activation patterns are different from the northern Hikurangi margin, suggesting that another triggering mechanism is active. We suggest that SSE-induced stress loading is a plausible mechanism of earthquake-triggering at the Southern Hikurangi margin. The regional difference we infer in earthquake-triggering mechanisms between the northern and central Hikurangi margins is consistent with other geological and geophysical features of fluid movement.