INSIGHTS INTO THE LATE INTERSEISMIC STATE OF THE ALPINE FAULT FROM MICROSEISMICITY AND TREMOR
The Alpine Fault in New Zealand is one of the most active transform faults and is currently in the late stages of its seismic cycle. Paleoseismic records show that it has ruptured four times in M7–8 earthquakes over the past 900 years, most recently in 1717 CE, with a ~75 \% probability of another rupture in the next 50 years. This poses a major hazard to central and southern New Zealand, making it critical to understand where the fault is locked and how strain is accumulating. We address this with two new interseismic seismicity catalogues spanning October 2021 to November 2023: an automatic microseismicity catalogue and a systematic tectonic tremor catalogue.
The microseismicity catalogue comprises 31,148 events (–0.0 to 4.9 ML), providing the first continuous along‐strike dataset for the Alpine Fault. We observe significant along-strike variability in seismogenic cutoff depths, on-fault seismicity, and off-fault seismicity, offering insights into where the fault is locked versus creeping. The tremor catalogue contains 336 events grouped into three clusters (Mt. Strachan, Haast River, Red Mountain), generally located just below the seismogenic cutoff. The location of these tremor clusters indicates where different segments of the Alpine Fault are accommodating strain aseismically during the late interseismic period.
Together, these catalogues provide the first high‐resolution view of ~450 km of the Alpine Fault, highlighting along‐strike variations in coupling and offering new constraints on rupture barriers, asperities, and how the next Alpine Fault earthquake may nucleate and propagate.