Low-Fequency Earthquakes Accompany Deep-Slow Slip beneath the North Island of New Zealand

Abstract:

Slow slip events have been observed along the Hikurangi subduction zone beneath the North Island of New Zealand. Slow slip occurs both in the shallow plate interface (<15km depth) and at the deeper end of the seismogenic zone (>30km depth). We present a systematically generated catalog of low-frequency earthquakes (LFEs) located within the central Hikurangi margin, beneath the Kaimanawa range. To detect LFEs from the continuous seismic data recorded by GeoNet, we used a matched-filter technique with template waveforms derived from previous observations of tectonic tremor. The workflow presented in this work is composed of 3 iterations of a matched-filter search. Each iteration, the detections were gathered into families and their common waveforms were postprocessed with machine learning to extract high-quality waveforms, allowing us to pick seismic phase arrivals to locate the LFEs. We found that LFEs are organized into episodes of intense activity during deep M7 slow slip events that occur every 5 years beneath the Kaimanawa region. We also observe a recurrence time of 2 years between other large bursts of LFEs, suggestive of a shorter cycle of slow slip. Finally, we expect that other frequent LFE episodes highlight smaller slow transients that have not yet been geodetically observed.