Long-range seismic activity detected using DAS technology installed on Madeira Island

Researchers taking part in the EC-funded SUBMERSE project have detected seismic activity over 4,500km away in Turkey

A team led by INESC TEC has used equipment installed on Madeira Island to detect seismic activity in Turkey, over 4,500km away. This is the first time that seismic activity has been recorded over such a distance using Distributed Acoustic Sensing (DAS) technology, and clearly illustrates the potential of the technology for detecting seismic events over long ranges.

The analysis took place between 31 January and 10 February 2023. The most notable event was a 7.8-magnitude earthquake on the Richter scale in Turkey on 6 February 2023, as shown in Figure 1 (above).

Although dated by over a year, this dataset marks the initial acquisition carried out using a DAS unit on the EllaLink cable located in Madeira Island. Given the specialised equipment employed (an HDAS from Alcalá University), the development of a tailored algorithm was necessary, which significantly extended the time frame. Moreover, accessing the data is currently restricted to physical means, delaying timely data processing. However, Portuguese partners are actively addressing this limitation and are confident of solving it in the near future. INESC TEC is one of the 24 partners participating in the European EC-funded SUBMERSE project, whose primary goal is to install DAS and State of Polarisation (SoP) technology in submarine cables to monitor and detect seismic activity in the deep sea.

This recent breakthrough demonstrates the capabilities of DAS technology in detecting seismic events and highlights its potential for early warning systems and improved monitoring of earthquake-prone areas. The team’s findings contribute to the growing research on using fibre optic cables as seismic sensors, opening new avenues for seismic monitoring and research. The SUBMERSE project aims to install equipment in Portugal, Greece, and Norway to store, process and analyse the data collected for geophysical purposes.

The group from INESC TEC, led by Orlando Frazão and including Susana Silva, Catarina Monteiro, and Cristina Cunha, installed a distributed acoustic sensor (HDAS – HiFi – Distributed Acoustic Sensor) at EMACOM’s Submarine Cable Station in Amparo, Madeira Island, to monitor seismic activity.

The HDAS, provided by the University of Alcalá in Spain, was set up on a fibre of the EllaLink cable. This made it possible to measure and record deformations along the 50km stretch of optical fibre. Thanks to FCCN’s collaboration, internet connectivity was available from the island to the mainland. INESC TEC’s system administration services, represented by Jaime Dias and António Carlos Sá, were crucial in ensuring data storage.

The data collected by INESC TEC’s team was then processed and analysed in partnership with Hugo Martins from IO-CSIC in Madrid, Spain, and provided valuable information for seismic monitoring research. Using fibre optic cables as seismic sensors, new possibilities for studying and understanding earthquakes are being explored.

The collaboration between the different institutions demonstrates the importance of international cooperation in advancing scientific knowledge.

Long-range seismic activity
Figure 2

Figure 2 displays the wavenumber spectrum as a function of the distributed acoustic detection frequency, illustrating the propagation of the earthquake through oceanic and seismic waves in the ocean. Although the earthquake was not felt in these regions, it was detected by seismic stations in Madeira, Porto Santo and the Canary Islands. The HDAS technology employed in these tests could also detect other long-distance and local events of lower magnitude.

This marks a significant advance in seismic monitoring capabilities through DAS technology using existing submarine cables. Furthermore, the technology exhibits high potential in the fields of oceanography and cetology, and its effectiveness in the structural monitoring of underground fibre optic cables has already been demonstrated.

The collaborative efforts between the partners under the SUBMERSE project have yielded valuable insights into seismic activity by using fibre optic cables as seismic sensors. By continuously monitoring and analysing the data collected, researchers can further our understanding of earthquakes and contribute to developing more effective monitoring and early warning systems.

Image captions

Main image: Time spectrum of the strain distribution measured along the 50 km of optical fibre. A high-intensity event is visible (10:32:46), corresponding to the earthquake detected in Turkey (6 February 2023).

Figure 2: Wavenumber spectrum as a function of the distributed acoustic detection frequency for 2 h of strain data measured on the 50 km of optical fibre: separation of ocean waves (vertical) and seismic waves (horizontal).

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