Reimagining Seismic Array Processing with Fibre-Optic DAS: The NORFOX Array

NORFOX is a purpose-built fibre-optic Distributed Acoustic Sensing (DAS) installation located in southeastern Norway, approximately 150 km north of Oslo. Beyond its primary function of monitoring earthquakes and explosions, the system captures a broad range of other signals, including aircraft, thunder, and atmospheric phenomena. A key advantage of NORFOX is its overlap with the co-located NORES seismometer array, which enables direct calibration of DAS measurements against conventional seismic recordings and supports method development under well-constrained ground-truth conditions. In this contribution, we introduce the NORFOX infrastructure and array layout, discuss key design choices, and summarize practical strengths and limitations using representative examples.

NORFOX is additionally equipped with all-sky cameras operated by Norsk Meteor Nettverk for meteor monitoring, which also capture nearby lightning activity. Lightning locations provide independent timing and spatial context that help interpretation coincident acoustic signatures observed on the fibre. Together with weather information, noise-floor characterization, and optical monitoring, these observations provide a benchmark dataset for both existing and future DAS installations and calibration

We also present in-house approaches to reduce noise, understanding signals, strategies on managing data volumes and edge-computing. Furthermore, we show and interpret signals from nearby quarry blasts, regional earthquakes, thunderstorms, and aircraft. Finally, we demonstrate and evaluate DAS array-processing methodologies for earthquake and explosion monitoring at NORFOX. Overall, dedicated research fibre arrays such as NORFOX provide a controlled environment to develop, benchmark, and calibrate DAS-based monitoring workflows in combination with co-located seismic instrumentation.