Geodynamics and Tectonics Plate Analysis based on Distributed Optical Fibre Acoustic Sensor

Megathrust earthquakes have long occurred repeatedly in Japan. Since 2011, an oceanic observation networks constituted by point sensors connected by optical fibres have been developed to monitor seismotectonic activities in this region. In this project we expand the seismometer capabilities by using the optical fibre network itself as a distributed seismometer providing thousands of high resolution seismic measurements aimed at clarifying the source of the very low frequency earthquakes based in the accretionary wedge between the Philippine Sea Plate and the Eurasian continent, which were discovered by the DONET stations in 2015.
After initial tesing in JAMSTEC own fiber optic cables off Toyohashi, Aichi, Japan and Hatsushima, Shizuoka, Japan, a portable unit will be manufactured and will be taken on the research vessel R/V Shinsei-maru to be connected to the 10 km fibre optic extension cables via a fibre optic cable of the shipboard remotely operated vehicle. The novel distributed seismometer will be tested in the DONET stations to produce a 3D map of seismic activity along the Nankai through and investigate possible links links with the structure of the subducting plate interface.

This project is a joint collaboration between the University of Southampton (UK) and the Japan Agency for Marine-earth Science and Technology (JAMSTEC), which is expected to have a wide range of impact, ranging from societal to commercial, from new scientific knowledge to providing true benefits to society at large.
A description of the different types of impact is detailed below.
1) Society
This project aims to impact society in a number of ways, that will result in major improvements in Quality of life. It could provide better understanding of seismic dynamics and improved monitoring technologies that might result in increased safety for all countries having population living in seismic prone areas. The outcome of this project might be used to improve earthquake and tsunami early warning systems, decreasing the number of fatalities and economic cost of dealing with seismic aftermath.
As for International Development, impact could also be significant. There are numerous country prone to earthquakes and related Tsunami and most of them are official development assistance (ODA) compliant; the deployment of the sensing technology developed in this project couldprovide seismic information in real time using the available telecom fibre networks.
This project might also have impact in terms of Policy, in particular regarding seismic monitoring and early warning systems, which would benefit from the waveform classification system developed here.
2) Economic
This proposal will deliver a new product: a long range distributed acoustic sensor that could find applications well beyond seismic monitoring: border security, smart motorways and railways, and intruder detection systems are jsut few examples. The advantage of our proposed system over conventional existing optical fibredetection systems is that our system will be able to fully identify the acoustic characteristics of the intruder, helping to identify not just the location, but also the type of intruder (i.e. people, animals, vehicles or other objects), or event (car collision, object falling on tarmac, damaged surface).
3) Knowledge
This proposal will provide scientific advances related to geophysics: the investigation of earthquake epicentre dynamic position and the relation between different seismic activities will be at the forefront. High-speed seismic measurements by the distributed acoustic sensor will be used to determine dynamic migration of seismic epicentre during seismic activities and create a dynamic mapping of the different types of seismic activities to the detailed seismic structure. The map of migration of seismic events in the tectonic structure could be used to assess varying stress state in the seismogenic plate interface where large earthquakes nucleates. The relation between the different seismic traces will include conventional earthquakes, low frequency tremors, slow slip events and very low frequency earthquakes.