Pre-commercial baseline passive seismic monitoring around CarbonNet's Pelican Site in the offshore Gippsland Basin, Victoria—The first five years

We undertook the design, development, and operation of a two-scale high-performance seismic network in SE Victoria to establish a baseline for natural seismicity around CarbonNet's Pelican Site. This is particularly important for providing assurance of the safety of the CO2 storage space and discriminating between natural and induced seismicity. The new high-precision earthquake catalogue developed from this work demonstrates a significant improvement in monitoring passive seismicity; a 77% average increase in annual event detections relative to pre-2017, magnitude of completeness lowered from 1.2 to 0.7, a minimum detection magnitude of -0.5, and location errors of ≤ ∼1 km within the network. Using the new earthquake catalogue, we also discovered the hitherto unknown deepest seismogenic zone in Australia in the offshore Gippsland Basin, with event depths exceeding 25 km. The spatial distribution of earthquakes indicates no seismic activity within a ∼10 km radius around the Pelican Site, providing confidence in its selection for potential CCS development. Together with the spatial distribution of earthquakes, newly estimated and more robust earthquake magnitude-frequency parameters enable the discrimination of natural versus induced seismicity with greater confidence. Continuous monitoring is recommended to overcome the limitations of the short monitoring time window.