Earthquake and tsunami detection using fibre optic cables

The National Seismic Network is working on the use of fibre optic cables to detect earthquakes and tsunamis in real time, study the structure of the shallow crust, and explore other potential applications of interest in the field of seismology.

In particular, Distributed Acoustic Sensing (DAS) using fibre optic cables opens new opportunities for seismic monitoring in unsafe or hard-to-access environments, such as urban areas, critical infrastructure, and marine settings.

Since 2020, the Instituto Geográfico Nacional (IGN) has been conducting several experiments in different geological contexts to evaluate the capabilities of this technique for earthquake and tsunami detection.

What is Distributed Acoustic Sensing (DAS)?

Distributed Acoustic Sensing (DAS)is a technique that enables continuous measurements of strain along a fibre-optic cable produced, among other possible phenomena, by the propagation of seismic waves. With this technology, optical fibre becomes a dense network of sensors capable of detecting earthquakes. Unlike traditional seismic sensors, which measure ground acceleration, velocity, or displacement at specific points, DAS provides measurements of strain or strain rate along the entire length of the optical fibre.

Advantages	Disadvantages and limitations
High spatial resolution (~m). High temporal resolution (~ KHz). High spatial coverage (up to 50 km). Possibility of using already deployed fibre-optic cables. Useful for urban areas and remote environments (oceans, volcanoes, glaciers, etc.) Avoids synchronization problems of sensor clocks.	DAS can only record strain rate in the direction along the fibre. Large data volume (~ TB / day). Difficult knowledge of the exactly coordinates of the cable position and its coupling with the ground.

How does DAS work?

A DAS interrogator is connected to one end of the fibre-optic cable, and laser pulses are transmitted through the fibre. As the pulses travel along the cable, a small portion of the light is backscattered toward the interrogator due to reflections and scattering caused by microscopic imperfections within the fibre core. When the position of these heterogeneities changes, a phase difference between the transmitted pulse and the backscattered signal can be measured, allowing cable elongations to be calculated.

Thus, this technology converts the optical fibre into an array of thousands of seismic sensors by sending laser pulses through the cable and recording their reflections and scattering with the DAS interrogator. Currently, numerous studies on DAS measurements can be found in the specialized literature, and the number of investigated applications continues to grow. In the field of seismology, several experiments have shown that both regional and teleseismic earthquakes can be successfully detected.
What are the acquisition parameters?
During data acquisition, the optical fibre is sampled in both space and time. The different parameters must be adjusted to ensure efficient acquisition depending on the characteristics of the experiment. Some of the most important parameters are:
- Fibre length to be interrogated.
- Optical power and pulse width to optimize the optical signal (i.e., the physical length of the pulse within the optical fibre).
- Interrogation pulse rate (number of pulses sent into the fiber per second).
- Spatial sampling resolution (distance between two consecutive sampling points along the optical fibre).
- Gauge length (signal integration length along the optical fibre).
- Derivation time (signal derivation time to compute the strain rate).

DAS experiments developed by the IGN

Distributed Acoustic Sensing (DAS) experiments carried out by the Instituto Geográfico Nacional (IGN) have been conducted in different seismotectonic regions. These data have been acquired using different types of equipment and both terrestrial and submarine fibre-optic cables.
These experiments have been carried out within the framework of national agreements (IGN–Adif) as well as international collaborations (IGN–University of Michigan and IGN–IRIS). The data obtained from these experiments are useful for recording earthquakes in inaccessible areas as a complement to conventional instruments.
In addition, these data have been used to determine properties of the shallow subsurface structure and to record teleseismic events using simultaneous global DAS deployments. The datasets from these experiments are available through FDSN web services or upon request at sismologia@transportes.gob.es.

Currently, the Instituto Geográfico Nacional (IGN) is involved in the FERMAT project (PID2024-162301OB-C21), coordinated by the Instituto de Ciencias del Mar and the Instituto de Óptica Daza de Valdés of the Consejo Superior de Investigaciones Científicas (CSIC), aimed at improving earthquake and tsunami detection in the Gulf of Cádiz using DAS and integrating this technology into the tsunami monitoring and early warning network of the National Tsunami Warning Center.

1. Mountain Range (high-speed railway)

MAIN CHARACTERISTICS OF THE EXPERIMENT:

Guadarrama Range tunnel (high-speed railway)
Fibre / interrogator	Location	Soto del Real-Segovia
	Dates	February 2023
	Fibre owner	Adif
	Cable deployment	subsoil pipe along high-speed railway
	Length interrogated	36 km
	Interrogator	Aragon Photonics (HDAS)
Mesurement	Duration of measurement	28 days
	Spatial resolution	10 m
	Number of channels	3600
	Sampling frequency	100 Hz
	Volume of data	2 TB
Results Fibre / interrogator	Minimum magnitude from recorded earthquakes	M 4.2
	Published research	Andreas Wuestefeld et al (2023). The Global DAS Month of February 2023. Seismological Research Letters, 95 (3): 1569–1577. doi: https://doi.org/10.1785/0220230180
	Data accessibility	FDSN: ZV (2023-2023): IGN-ADIF Traintrack, Central Mountain Range (Spain). DAS_MONTH experiment

FIBRE LOCATION:

RESULTS:

2. Sedimentary Basin (high-speed railway)

MAIN CHARACTERISTICS OF THE EXPERIMENT:

Sedimentary basin (high-speed railway)
Fibre / interrogator	Location	Granada -Íllora
	Dates	June-September 2022
	Fibre owner	Adif
	Cable deployment	subsoil pipe along high-speed railway
	Length interrogated	36 km
	Interrogator	Aragon Photonics (HDAS)
Mesurement	Duration of measurement	82 days (discontinuous)
	Spatial resolution	10 m
	Number of channels	3600
	Sampling frequency	100 Hz
	Volume of data	3 TB
Results Fibre / interrogator	Minimum magnitude from recorded earthquakes	M 0.8
	Published research	Canudo J., et al. (2025) Ambient Noise Interferometry using Chirped-Pulse DAS data for subsurface exploration. 29th International Conference on Optical Fiber Sensors. 2025 Porto, Portugal. Extended Abstract. Preciado-Garbayo J., et al. (2025) Chirped-Pulse DAS as a seismic surface wave monitoring tool along trackside dark fibers: application in the analysis of superstructure features. 29th International Conference on Optical Fiber Sensors. 2025 Porto, Portugal. Extended Abstract
	Data accessibility	On request sismologia@transportes.gob.es

FIBRE LOCATION:

RESULTS:

Local earthquake, M 1.9, Granada, Spain 2022/07/02

Teleseismic event, M 7.7, Mexico 2022/09/19

3. Mediterranean sea (submarine cable)

MAIN CHARACTERISTICS OF THE EXPERIMENT:

Mediterranean sea (submarine cable)
Fibre / interrogator	Location	Valencia-Mallorca
	Dates	September 2020
	Fibre owner	ISLALINK
	Cable deployment	submarine cable buried at 1 m
	Length interrogated	50 km
	Interrogator	Febus (A1-R)
Mesurement	Duration of measurement	14 days
	Spatial resolution	16,8 m
	Number of channels	2977
	Sampling frequency	1000 Hz
	Volume of data	40 GB/h
Results	Minimum magnitude from recorded earthquakes	M 3.6
	Published research	Xiao, H., Tanimoto, T., Spica, Z.J., Gaite, B., Ruiz-Barajas, S., Pan, M., & Viens, L. (2022). Locating the precise sources of high-frequency microseisms using distributed acoustic sensing. Geophysical Research Letters, 49, e2022GL099292. doi: https://doi.org/10.1029/2022GL099292
	Published research	Spica, Z. J., J. AjoFranklin, G. C. Beroza, B. Biondi, F. Cheng, B. Gaite, B. Luo, E. Martin, J. Shen, C. Thurber, et al. (2023). PubDAS: A PUBlic Distributed Acoustic Sensing Datasets Repository for Geosciences, Seismol. Res. Lett. 94, 983–998, doi: 10.1785/
	Data accessibility	FDSN: ZH (2020-2020): The Valencia-Islalink Distributed Acoustic Sensing Experiment

FIBRE LOCATION:

RESULTS:

4. Granada city (telescope cable)

MAIN CHARACTERISTICS OF THE EXPERIMENT:

Granada city (telescope cable)
Fibre / interrogator	Location	Granada IRAM-Telescope Veleta peak
	Dates	August 2020
	Fibre owner	IRIS
	Cable deployment	subsoil pipe
	Length interrogated	20 km
	Interrogator	Febus (A1-R)
Mesurement	Duration of measurement	23 hours (discontinuous)
	Spatial resolution	4,8 m
	Number of channels	4166
	Sampling frequency	2000Hz
	Volume of data	5,7 TB (240 GB/h )
Results	Minimum magnitude from recorded earthquakes	None earthquake recorded
	Published research	Li, Yang , Perton, M., Gaite, B., Ruiz-Barajas, S. and Spica, Zack. (2023). Near-surface characterization using Distributed Acoustic Sensing in an urban area: Granada, Spain. Geophys. J.Int, 235, 1849-1860, doi: 10.31223/X5266C.
	Published research	Benjumea B. et al. (2021). DAS dataset analysis for reflection imaging with ambient noise in urban areas: Granada, Spain. European Association of Geoscientists & Engineers, doi: https://doi.org/10.3997/2214-4609.202120147
	Data accessibility	On request sismologia@transportes.gob.es

FIBRE LOCATION: