A Look at Two TsunamisA Look at Two Tsunamis on the BC Coast on the BC Coast with the Neptune-Canada Tsunami-meterswith 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 TeamSteven Mihaly (IOS)

BPR (Bottom Pressure Recorders)BPR (Bottom Pressure Recorders)

PGC in collaboration with Bennest Enterprises

developed 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

NEPTUNE TSUNAMIMETERNEPTUNE 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

Samoan EarthquakeSamoan Earthquake Chilean EarthquakeChilean Earthquake

200 km south of the Samoan Islands Offshore Maule, Chile

Tuesday, September 29, 2009, 17:48:11 UTC

Saturday, February 27, 2010, 06:34:14 UTC

Mw=8.0

(indicating 1/16th of the energy released in the Chilean earthquake)

Mw=8.8

(6th strongest Earthquake since 1900, highest Tsunami wave energy in Pacific since 1964)

Tsunami travelled 8300km to arrive at the Neptune array 11 hours later, averaging 755km/h

Tsunami travelled 10,650km to arrive at the Neptune array 16 hours later, averaging 666km/h

Well defined narrow band (9-13min) wavetrain with trough to crest height ~5cm

Broad band wave energy (5-150min) max trough to crest wave height ~6cm

Major Tsunamigenic Earthquakes in the Major Tsunamigenic Earthquakes in the Pacific since DeploymentPacific since Deployment

Northwest BPR

CORK BPR

South BPR

SAMOAN TSUNAMISAMOAN 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)

10km

BPR Antenna

IOS Regional Tsunami Numerical IOS Regional Tsunami Numerical ModelModel

•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

140km

120km

80km

Neptune-Canada BPR array

Comparison between observations and model

Data

Model

38 min

26 min

20 min

cm

02/24 02/25 02/26 02/27 02/28 03/01 03/02 03/03 03/04 03/05-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

15min ticks

deci

bar

CHILEAN TSUNAMICHILEAN TSUNAMI

DATADATA (DMAS Related Issues)(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

de

cib

ar

Pre-event wave energy

Seismic energy

140min

4.5h data gap resulting in unreliable data for ~day

10 Day Section of Tide-removed filtered pressure from BPR 1026 S

18h Zoom from 27-Feb 20:46:43 to 28-Feb 14:36:46, 2010

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.

Port Alberni (eigenfreq=120min)

Comparison of the two Tsunamis at Tidal StationsComparison of the two Tsunamis at Tidal Stations

•Although open ocean wave heights for the two Although open ocean wave heights for the two events were similar, the coastal responses were events were similar, the coastal responses were functions of the specific features of the two tsunamisfunctions of the specific features of the two tsunamis

Vertical Scale3:1

50 cm

Prince Rupert

•The BC coast acts as an active “transfer function” for incoming tsunami waves

• Note: no data gaps in 20 records!

150min

25 min

120min

50min

110min

FIN