In 2019, AP Sensing’s DAS system was used for preliminary earthquake observations and research at the University of Tokyo. Data was collected throughout a period of 46 hours for seafloor observation; many micro-earthquakes were recorded as well as one deep earthquake below the Sea of Japan. One DAS interrogator unit was installed temporarily in the landing station and data was collected over 100 km with a spatial resolution of 5 m and sampling frequency of 500 Hz. The data from the DAS measurement will be used in a comparison with data from seismometers of the Sanriku seafloor observation system.
AP Sensing’s DAS system detects vibrations and captures acoustic energy along the optical fiber with high sensitivity. Utilizing Coherent Optical Time Domain Reflectometry (C-OTDR), Rayleigh backscattering detects acoustic frequency signals over long distances. The DAS interrogator sends a coherent laser pulse along the sensor cable, and acoustic disturbances generate micro strains within the fiber, which cause a change in the phase relation and/or amplitude.
DAS is capable of real-time and long-term seismic monitoring with a spatial sampling of only a few meters, which is a significant improvement compared to traditional methods. In marine environments, DAS is incredibly useful for the study of plate movement and generation of earthquakes and tsunamis. Additionally, distributed fiber optic sensing is a cost-effective solution for the number of sensing points that it monitors over distances which can span dozens of kilometers, which is another superiority of the technology.
Fiber optic cable is already installed across the globe for other purposes, and the solution is easy to deploy, resilient in harsh environments, low maintenance, operates remotely, and has a long lifespan. Technological advances combine DAS with machine learning for greater sensitivity to specific environmental events. These benefits offer a unique monitoring platform for seismic monitoring and disaster mitigation.