1. Cabled systems for near-field tsunami early warning: An observation system simulation experiment (OSSE) offshore Portugal
A. Babeyko1, M. Nosov2 and S. Kolesov2
1 GeoForschungsZentrum Potsdam
2 Moscow State University, Physical Dept.

2. Tsunami Early Warning: Far Field
SIFT – Short-term Inundation Forecasting for Tsunamis (Titov et al., 2005)
1- DART buoys network
3- Invert for source using tsunami observations at DART BPR
2- Precompute tsunami waves from ‘unit sources’

3. Tsunami Early Warning: Coming closer to the source
DART55015
July 15, 2009 M7.8
Seismic waves
NOISE !!!
Tsunami
Australian DART55015 buoy is located ca. 500 km from the epicenter (about 30 min tsunami runtime).
In this case even at 500 km noise amplitude from Mw=7.8 is comparable to the tsunami signal!

4. Tsunami Early Warning: Coming closer to the source
Butler et al (2014): ITU/UNESCO-IOC/WMO Joint Task Force on Green Cables Report
Figure from NOAA PMEL
Resume: DART I-III with 15 sec sampling rate have limited use in the near-field
→ High sampling rate is needed to filter out the gravity wave

5. Solution 1: stand-along OBS
Tsunami Early Warning in the Near-Field: technology must provide high sampling rate of BPR records
Solution 1: stand-along OBS

6. Tsunami Early Warning in the Near-Field: technology must provide high sampling rate of BPR records
Solution 2: cabled OBS
DONET 1+2: Cabled systems in Japan

7. 3- Optimized DART positions
Observation system simulation experiment (OSSE) offshore Portugal Motivation
Omira et al. (2009): Design of a Sea-level Tsunami Detection Network for the Gulf of Cadiz
2- Virtual DART positioning by “warning time” optimization
3- Optimized DART positions
1- Rupture scenarios
Simulations done in shallow-water approximation (COMCOT) assuming static rupture model (Okada’85)

8. Observation system simulation experiment (OSSE) offshore Portugal Motivation
How DART bottom-pressure sensor signal could look like in a more realistic simulation? ?
For more realistic simulations we will use: (1) kinematic source model (“shaking source”) and (2) non-hydrostatic full 3D wave propagation model

9. Static (final) uplift of the sea bottom
Observation system simulation experiment (OSSE) offshore Portugal Simulation method
1) Kinematic rupture model
Sea bottom shaking due to M8.0 earthquake simulated with code QSGRN/QSCMP (Wang et al., 2008)
under Buoy-1
under Buoy-1
Static (final) uplift of the sea bottom
static
under Buoy-3
under Buoy-2

10. Observation system simulation experiment (OSSE) offshore Portugal Simulation method
2) Non-hydrostatic compressible 3D fluid model (linear potential theory)
(Nosov and Kolesov, 2007)
F(x,y,z,t) – 3D velocity potential
n – unit normal to the sea bottom

11. Kinematic rupture + full-3D ocean
Observation system simulation experiment (OSSE) offshore Portugal Results
Sea surface evolution at Time = 0 sec
Static uplift + SWE
Kinematic rupture + full-3D ocean

12. Kinematic rupture + full-3D ocean
Observation system simulation experiment (OSSE) offshore Portugal Results
Sea surface evolution at Time = 60 sec
Static uplift + SWE
Kinematic rupture + full-3D ocean

13. Kinematic rupture + full-3D ocean
Observation system simulation experiment (OSSE) offshore Portugal Results
Sea surface evolution at Time = 120 sec
Static uplift + SWE
Kinematic rupture + full-3D ocean

14. Observation system simulation experiment (OSSE) offshore Portugal Results
Buoy-1
Bottom pressure unit under Buoy-1
Acoustic + seismic ‘noise’
Pressure (Pa) variations can be re-computed into effective surface wave height (m) using:
p = gh
Which means factor 10⁻⁴
Variations of bottom pressure due to acoustic and seismic ‘noise’ correspond to ~300 m of effective wave height !!!
Two orders of magnitude larger than tsunami wave height!
Tsunami wave
low-pass filtered
Note the scale: 2 orders of magnitude smaller!

15. Observation system simulation experiment (OSSE) offshore Portugal Results
Buoy-2
Bottom pressure unit under Buoy-2
low-pass filtered

16. Observation system simulation experiment (OSSE) offshore Portugal Results
Buoy-3
Bottom pressure unit under Buoy-3
low-pass filtered

17. Observation system simulation experiment (OSSE) offshore Portugal
Conclusions
We have conducted numerical experiment of tsunami wave generation and propagation using kinematic rupture modeling coupled with full 3D compressible fluid simulations with the goal to simulate pressure variations at OBU units located in the source near-field
Pressure variations due to acoustic and seismic ‘noise’ are two orders of magnitude larger than the tsunami wave amplitude
Tsunami wave can still be detected after low-pass filtering
Filtering ultimatevely requires high-rate sampling at OBU
High-rate sampling can be provided by cabled systems or last-generation DART 4G