1. Tsunami Detection?
April 2016

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

3. 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

4. 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?

5. 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.

6. 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?

7. 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)

8. 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 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?

9. 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