A study featured in Geophysical Journal International outlines a solution that incorporates a straightforward physics-based algorithm alongside fibre optic measurements and conventional seismometer data. The researchers say that this advance could be integrated into existing early warning systems, as well as help pinpoint seismic events tied to erupting volcanoes, geothermal operations, or glacier activity.
Not only can this "exciting" breakthrough augment conventional quake-alert mechanisms, it also holds promise in monitoring a wide range of seismic phenomena.
"The ability to turn fibre optic cables into thousands of seismic sensors has inspired many approaches to use fibre for earthquake detection. However, fibre optic earthquake detection is not an easy challenge to solve," said lead researcher Dr Thomas Hudson, a senior research scientist at ETH Zurich.
"Here, we lean on combining the benefit of thousands of sensors with a simple physics-based approach to detect earthquakes using any fibre optic cable, anywhere."
"Excitingly, our method can combine fibre optic and traditional seismometer measurements, allowing fibre optic sensing to be included in existing earthquake early warning systems."
Known as distributed acoustic sensing (DAS), the technique transforms fibre optic lines into multiple acoustic and vibration sensors, useful for monitoring pipelines, railways, or subsurface movements. When applied to earthquake observation, DAS could tap into well-established fibre optic cables that span dense population centers and even cross oceans, making them prime candidates for significantly bolstering current seismic surveillance.
Real-world implementation, though, is not straightforward. Fibre cables follow layouts determined by urban infrastructure or geography, and seismologists cannot choose or alter these geometries. Furthermore, a city's ambient noise makes it harder for fibre-based readings to distinguish genuine tremors from random vibrations. Another complication is that DAS readings capture strain only along the cable's axis, whereas traditional seismometers measure three-dimensional ground motions. Because fibre optic cables on the surface are more responsive to S-waves than faster P-waves, they face difficulties pinpointing the earliest seismic signals.
One potential fix is to fuse inputs from traditional seismometers with DAS outputs, yet these distinct instruments differ in measurement units and sensitivity. Another hurdle is the sheer volume of data produced by thousands of fibre sensors, which requires swift, efficient processing to be of value in real-time earthquake detection.
The new algorithm addresses these issues by "migrating" recorded energy from fibres and seismometers backward in space and time, identifying coherent peaks that may represent true earthquake events. This same physics-based method has also shown promise in tracking seismic disturbances linked to volcano eruptions, geothermal well operations, and glacier icequakes.
"A key strength of this physics-based approach is that it works well even in noisy environments, since noise is generally less coherent than an earthquake signal," said Dr Hudson.
"It can also be applied out-of-the-box to any fibre network."
He added: "Although we don't claim to have completely solved the large data volume issue, we present pragmatic ways to deal with this and our algorithm runs in real time for the datasets tested.
"The method is provided open-source, so that the wider seismology community can immediately benefit."
Research Report:Towards a widely applicable earthquake detection algorithm for fibreoptic and hybrid fibreoptic-seismometer networks
Related Links
Department of Earth and Planetary Sciences at ETH Zurich
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