Tsunami Detection? April 2016

What can be done and what can’t (easily) Stuart Barnes, Joerg Schwartz, Steve Desbruslais and Maria Ionescu

Earthquakes, Impact and Detection What are the tell-tale signals on the seabed Temperature drops Pressure changes Underwater waves Shock waves Large external temperature changes can be detected internally, but not the changes likely to be seen remote from the epicentre Underwater waves are only detected if they move/shake the repeater Pressure changes can only be detected outside the repeater due to the hermetic characteristics Only an outside shock effect can be truly detected “inside” a repeater

Benefit and impact of having internal devices Temperature and shock detection both feasible However there needs to be some form of continuous active supervisory to trigger alerts at NMS in real-time There is some impact on cost but minimal impact on installation and usage (and may in fact give a commercial opportunity to cable owners) BUT do we know what we are really trying to detect?

Accelerometer measurements from deep sea trial We have already had experience with accelerometers in determining the path of a repeater during deployment and errors in the usual algorithm to determine where the repeater will land.

The impact of external devices Any external sensors would have to be located on the Bulkhead or on a cable streamed away from the repeater More sensitive devices can be housed externally. But, There is little “real estate” on a small repeater A third cable solution may look like that of a Branching Unit (See opposite) This approach will have major cost and risk impacts over and above a standard deployment Are there smarter ways for detection with less impact?

What are the signatures of an earthquake? Temperature Pressure Shock waves Primary (P) waves (longitudinal) Secondary (S) waves (transverse) Surface waves (LR) (damaging) 3D accelerometers are sensitive to all types of shock waves. P-waves (compressional) arrive first and can provide critical tsunami warning-time. Seismogram from IRIS (Incorporated Research Institutions for Seismology) http://www.geo.mtu.edu/UPSeis/waves.html

Earthquake shock waves travel at least 10x faster than tsunami waves. Shock Detectors Earthquake shock waves travel at least 10x faster than tsunami waves. Shock waves detection can thus provide an early warning mechanism. The transmitted frequencies of interest are 0.01-0.1 Hz, for shock waves of earthquakes of magnitude > 6. Accelerometers are ideal sensors for: Large local earthquakes High-frequency seismic waves A variety of accelerometers can be sourced with different frequency responses, within a frequency band of 0-100Hz. What is needed?

Concluding Remarks Accelerometers can be placed inside repeaters as a possible means of providing Tsunami warnings These can be installed with little installation and operational risk and may provide a source of additional revenue to an operator External sensors are much more problematical both from an installation and maintenance perspective Active supervisory solutions are needed to feedback information Our supervisory system sends data in both directions so it will automatically arrive at the closest land point first The frequency response range is unknown But if this be shown to work then this is a very low cost/easy to implement solution