Distributed Acoustic Sensing for Seismic Monitoring of the Flores Thrust, Indonesia

Indonesia faces a unique combination of exposure to tsunamis, with dense coastal populations, intense seismic and volcanic activity, and multiple tsunami-generation mechanisms that can threaten shorelines with very little time for reaction.

BMKG which is in charge of monitoring tsunamis faces 2 limitations: First, the operational system still relies mainly on land-based seismology, coastal sea-level observations, and precomputed modelling, while the availability and operability of deep-ocean buoy observations have remained an ongoing issue. Second, the existing system was designed for tectonic earthquake-generated tsunamis and is not sufficient on its own for non-tectonic sources such as volcanic or landslide-triggered events.

To address these limitations, BPPT (subsequently integrated into BRIN in 2021), initiated the planning, design, and deployment of two prototype Ocean Bottom Unit (OBU) sensors between 2020 and 2022. The deployed units integrate high-sensitivity accelerometers and static pressure sensors to enable real-time monitoring of seismic activity and tsunami wave propagation in the northern waters of Labuan Bajo, Flores.

The first OBU was installed approximately 25 km offshore at a depth of 2,110 m, whereas the second unit, positioned at the terminal section of the submarine cable, was deployed approximately 55 km offshore at a depth of 4,122 m. Both installations were strategically designed to monitor seismic activity associated with the Flores Thrust, located roughly 100 km north of Flores Island. Historical earthquakes along this tectonic structure, together with the submarine landslides they triggered, generated destructive tsunamis in 1982 and 1992, resulting in significant casualties and coastal run-up heights exceeding 20 m.

The deployed submarine cable system has a total length of 55 km and incorporates 12 optical fibres, providing the necessary infrastructure for integrated sensing and real-time data transmission. At the end of April 2026, we connected a Febus Optics A1 DAS interrogator to one of the fibres for a preliminary study of local and regional seismicity. Our objectives with this initial deployment are to catalogue and characterise local seismicity, locate sources, and investigate improvements in the location of local earthquakes by using a combination of land-based seismic stations and the undersea optical cable.