Insights into earthquake ruptures from analysis of DAS data

The possibility to exploit fibre optic cables through Distributed Acoustic Sensing (DAS) systems is a powerful tool for seismologists, providing spatially continuous recordings of earthquakes. This technology is suitable for the analysis of seismic ruptures, continuously mapping the source properties as observed along the sensed cable. In this study we describe how far-field strain radiation from a circular rupture can be modelled to evaluate the earthquake size and released stress drop during fault slippage. We then fit earthquake signals recorded along a 150 km long dark fibre cable deployed offshore the coast of Central Chile sensed by DAS, to evaluate the rupture properties of small to moderate subduction events. We show that stress drop increases for moderate magnitude events, indicating a complexity in the slip pattern and the presence of small scale asperities also at this scale.