Real-time Observation of Tsunamis on the BC Coast

1. A Look at Two Tsunamison the BC Coast with the Neptune-Canada Tsunami-meters Richard Thomson (PI-IOS) Isaac Fine (Modelling-IOS) Alexander Rabinovich (Long Waves-IOS) Martin Heeseman (PGC) Earl Davis (PGC) Maxim Krassovski (IOS) NEPTUNE Science DMAS Team Steven Mihaly (IOS)

2. NEPTUNE TSUNAMIMETER 3 BPR array in 2600m surrounding the BPR at ODP Borehole 1026; the NE leg not deployed. ODP 889: 1260m Barkley Upper Slope: 400m Folger Deep: 100m Failed: Folger 27-Nov; NW 21-Feb BPR (Bottom Pressure Recorders) PGCin collaboration with Bennest Enterprisesdeveloped a novel way to process data from Paroscientific Digiquartz pressure sensors substantially enhancing pressure resolution. This, along with the Cabled observatory enabled high temporal resolution gives us an unprecedented look at both seismic and oceanic waves in real-time 1 sec sampling, 0.4Pascal (~0.04mm ocean depth), 5microK. DART: 15min -> 15s acoustic modem-> satellite

3. Major Tsunamigenic Earthquakes in the Pacific since Deployment

4. BPR Antenna • SAMOAN TSUNAMI • Primary arrival consisted of 4 ~5cm waves with decreasing times between wave crests of 12min 50s, 10min 54s and 9min 54s, following waves were reduced to 2-3cm. • With waves traveling in this direction the arrival times at the array nodes were only separated by ~30s - 1min. The third leg arrival time would be 4.5min later and thus greatly improve accuracy. It would also enable error estimation, or possibly test the plane wave assumption. • Using the three BPR array and shallow water wave dynamics, wave characteristics could be estimated. (100km wavelength travelling 170km/h at 56 deg azimuth) Northwest BPR CORK BPR South BPR 10km

5. IOS Regional Tsunami Numerical Model • Driven by the BPR tsunami data; model initialized using the first observed tsunami waves transposed to the boundaries • A no-frills model optimised by Isaac Fine to run quickly based on the linear shallow water equations • Grid spacing 180m x 160m, very sensitive bathymetric accuracy Comparison between observations and model Data Model 20 min cm Neptune-Canada BPR array 26 min 80km 120km 140km 38 min

6. 10 Day Section of Tide-removed filtered pressure from BPR 1026 S • CHILEAN TSUNAMI • DATA(DMAS Related Issues) • Improvements: most BPRs were recording, so that pre-event pressure spectra can be generated; seismic waves were recorded. • Demerits: array no longer functional, NW BPR stopped recording 6 days prior to the event, giving rise to less accurate wave representation for the Regional Tsunami model; data gaps greatly affect processing • WAVE CHARACTERISTICS • Marginally larger (6 cm amplitude) waves compared to Samoan tsunami; ringing for half a day. • Elevated energy for at least 3 days • Complex Wave train with wave groups of 5-6, 9-13 min (as in Samoan) waves superposed on much longer 120-140 min waves 4.5h data gap resulting in unreliable data for ~day Seismic energy Pre-event wave energy decibar 18h Zoom from 27-Feb 20:46:43 to 28-Feb 14:36:46, 2010 140min

7. IOS Regional Tsunami Model • Both the complexity of the wave and the loss of BPRs in the array limited our ability to extrapolate the observed pressure at 1026B to a wave at the model boundaries • The modelled tsunami has spatially variable skill such that one pressure record at neighbouring pairs can be well represented whereas the other not; likely a result of inaccurate bathymetry.

8. Comparison of the two Tsunamis at Tidal Stations • Although open ocean wave heights for the two events were similar, the coastal responses were functions of the specific features of the two tsunamis Prince Rupert 110min • The BC coast acts as an active “transfer function” for incoming tsunami waves • Note: no data gaps in 20 records! Vertical Scale 3:1 50min Port Alberni (eigenfreq=120min) 120min 50 cm 150min 25 min

9. FIN