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.

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’

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!

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

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

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

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)

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

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

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

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

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

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

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!

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

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

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