Paleo-tsunami record and tsunami hazard in Wallis and Futuna Geoffroy Lamarche, NIWA, Wellington...
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Transcript of Paleo-tsunami record and tsunami hazard in Wallis and Futuna Geoffroy Lamarche, NIWA, Wellington...
Paleo-tsunami record Paleo-tsunami record and tsunami hazard and tsunami hazard in Wallis and Futunain Wallis and Futuna
Geoffroy Lamarche, NIWA, Wellington
James Goff, University NSW, Sydney
Bernard Pelletier, IRD, Nouméa
STAR Meeting 16-18 October 2010 Nadi, Fiji
Outline Outline • Geodynamic and Seismology• Historical Earthquakes• Impact of Sep 2009 tsunami• Palaeo-earthquake research
Futuna
165oE 180o
10oS
20oS
Geodynamic of the SW PacificGeodynamic of the SW Pacific
NouvelleCalédonie
FijiVanuatu
Tonga
Kermadec
Futuna
SeismicitySeismicity
130 ≥M7 44 ≥M7.5 18 ≥M7.8 7 ≥Mw8,
Depth : 0 - 700 km,20% of world seismicity in SW Pacific
Samoa
One earthquake > M 5,5 every 7 years on average
date M km to Léava
1977 03 23 6.3 281986 03 27 6.0 201993 03 12 6.4 141993 03 12 5.5 41999 09 17 5.5 13
1973-2009: 16,300 EQs 5≥ M ≥ 8.1
Tsunamis since 1992
PNG, Fat. 2200
Nov. 26, 1999VanuatuMax. runup : 7 mFatalities : 5
Sep. 30, 2009SamoaFatalities : 200
April 1, 2007Solomon IslandsMax. runup: 10mFatalities: 60
Dec. 26, 2004West SumatraMax. runup: 50mFatalities: >250,000
• 260 km west of Wallis• 600 km West of Samoa• 400 km NE of Fiji
Fiji
WallisFutuna Samoa
Futuna and Alofi
Tonga
Futuna -80 km2 (18x5 km)-515 m high-4500 habsAlofi-30 km2
-No habs
12 March 1993 MW6.4 Earthquake
All 100 y.o. churches collapsed
traditional falés unaffected
Destruction of houses on piles acceleration > 1G
Mesures Pelletier, 1999
Reverse fault
Uplifted coral
(Observations B. Pelletier, 1999)
Uplift
12 March 1993 MW6.4 Earthquake
12 March 1993 MW6.4 Earthquake (MM VIII)
SMarch 1993March 1993
Modelling : 2.73 m slip
St Pierre Chanel St Pierre Chanel (1803-41) describes an EQ in 1841 similar to that of March 93 (34 h fore-shock sequences, 19 severe quakes in 24h, after-shocks for 2 months).
Recurrence Recurrence : 70 yrs without aseismic slip
150 yrs based on last 2 events 50% aseismic movement
Fiji
Wallis
FutunaSamoa
Tonga
185 km ENE of Hihifo, Tonga190 km S of Apia, Samoa710 km NNE of Nuku’Alofa, Tonga2700 km NNE of Auckland
29 Sep 17:48 UTC 06:48:10 AM at epicenter 30 Sep 05:48 AM in Futuna & Fiji650 km from Futuna
2009 SouthWest Pacific (Tonga) Earthquake, MW 8.0
Futuna post-tsunami Survey
• EQ occurred at 5:48am on 30 Sep. local time in Futuna, ~650 km west of epicentre.
• PTWC issued warning at 6:04am for tsunami arrival in Wallis at 6.35am.
• No warning by authorities for Wallis & Futuna • No reported tsunami on Wallis. • Tsunami hit the Futuna between 7.00 and
7.20am • The tide was approximately 3/4 out.
Evidence of the 2009 tsunami
•Debris on road and beaches•Rocks moved•Salt-burnt grass and leaves•Broken branches •Debris held in bushes and trees•Interviews of people•Videos•photos
Run-up heights and Inundation distances measured for the 2009
tsunami
LéavaLéava
Is there a local effect from the topography of the bay ?
River is clearly fault controlled (“the sea is travelling beneath the house, and sprouting in the Taro crops behind the village!”)
Palaeo-tsunami research aims at identifying past events through geological evidence observed in trenches
Event 1 – 1860-2000 BPEvent 1 – 1860-2000 BPEvent 2- ca. 470 BPEvent 2- ca. 470 BP
The Legend of FatuloliKo le fonu tu'a limulimua
Oral traditions speak of deadly events which devastated the coast, and may be tsunamis
Daniel Frimigacci, 1995 "La Tortue au dos Moussue"
Can we find evidence?Can we date it more precisely ?Can we associate it to a tsunami ?
Futuna event chronologies and
selected potential source areas.
A - Austral Is., CI - Chatham Is., CkI - Cook Is., F - Futuna, H - Henderson Is., h - Healy caldera, Hu - Huahine, Society Is., K - Kauai, Hawaii, Ku - Kuwae, M - Marquesas, S - Samoa, V - Vanuatu.
direction of ~ max. wave energy in deep water away from subduction zone sources
Conclusion Conclusion Tsunami Hazard in FutunaTsunami Hazard in Futuna
• Paleo-tsunami (trenches & legend of Fatuloli)
• Local tsunami (March 1993)
• Submarine landslides offshore Léava
• Regional tsunami (Sep 2009)
• The 1993, 2009 events and oral tradition indicate that the tsunami hazard is high
• People (density 55) living exclusively on a 50-400 m-wide coastal strip
• Tide gauge will be installed in 2009
• Alarm in Futuna must be independent than that of Wallis !
What about tele-tsunami (Chile 1700) ?