MONITORING, DETECTING AND WARNING OF TSUNAMIS IN NORTH EAST ATLANTIC AREA

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Baptista M A, Matias L., Carrilho F. , Annunziato A. , J.M.Miranda, Omira, R

The vulnerability of North East Atlantic coastal areas to tsunamis is well known and the need for an early warning system is recognized by national authorities of the member states in the area. After the Sumatra tsunami of December 2004 the IOC UNESCO decided to implement a global tsunami warning system in 4 broad areas: the Indian Ocean, the Pacific Ocean, the Caribbean and the North East Atlantic, Mediterranean & connected seas

AZ GF SWI Tsunami events that affect Portugal mainland Azores and Madeira islands are originated along the Eurasia-Nubia plate boundary, between the Azores and the Strait of Gibraltar. This region can be divided in three main areas : the Azores area, the Gloria Fault, and the south west Iberia domain The responsibility of Portuguese national Tsunami Warning System (PtTWS) is to monitor this tsunamigenic area and give alert messages to the coastal areas of Portugal mainland and the archipelagos of Madeira and Azores.

The oldest event reported in historical documents dates 60BC The oldest Paleo-Tsunami 7000 BP (Huelva Spain)

At least 2 transoceanic events 1941.11.25

M8.2

1975.05.26

M7.9

Lisbon

1761.03.31

1755.11.01

1969.02.28

M8.0

Gulf of Cadiz Rabat

20 th Century events 3 M8 earthquakes – 3 tsunamis recorded more than 100 km away from the source Amplitudes ≥ 0.5 m 1941.11.25

M8.2

1975.05.26

M7.9

Lisbon

1761.03.31

1755.11.01

1969.02.28

M8.0

Rabat

NEAM DECISION MATRIX (Atlantic)

Operational Components of Pt TWS

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The development of the Pt TWS comprises sequential operations of data collection and analysis from the onset of the earthquake to the issuing of messages to the PTCivil Protection 3 Main components: Seismic Detection Tsunami Detection/Analysis Issue of Messages Host Institution: IM (Instituto de Meteorologia) operating 24X7 (it is responsible for the seismic network) IM (Lisbon) is the NATIONAL TSUNAMI FOCAL POINT for the NEAMTWS

Requirements of the PtTWS

Tsunami travel times to 1 st point at the coast in the Gulf of Cadiz is 21-30 min According to IOC-UNESCO a community is considered protected if the warming time is at least 15 minutes.

Pt TWS should confirm that a tsunami has been generated only six minutes after the onset of the earthquake

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Seismic Network

The seismic technology is the first one to be used in the detection of a possible tsunamigenic earthquake35 broad band stations + 22 SP enhanced , transmitting in real time with a latency less than 10 seconds, and 22 enhanced short period stations, transmitting in near real time (latency of approximately 2 minutes) using VSAT and internet. Data collected at IM includes also real-time data provided by other institutions (IGN, Spain, CNRST, Morocco)

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The seismic information collected is processed in near real time using a technical solution mixing SEISCOMP (Hanka et al. 2000) and SEISAN (Havskov and Ottemoler 2005) platforms, enabling the first computation of epicenter and magnitude in approximately 5 minutes after the event onset.

Hypocenter Location & Magnitude Estimates within 5 minutes

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The first message is based exclusively on seismic information; Once the TAT is triggered a tsunami scenario is selected from the pre-computed scenario database. The geographical coverage of the installed database covers the area extending west to the Azores towards the strait of Gibraltar; 6000 scenarios 6.5 < M< 8.75 (interval 0,25)

1st Message to Civil Defence

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When the first information (based on seismic data ) is received by the TAT it triggers the 1 st message to the civil protection including :

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ETTT – estimated tsunami travel time MTA – maximum tsunami amplitude at the previous selected forecast points along the Portuguese coast

Tsunami Monitoring

The present sea-level detection network includes solely coastal tide stations from Portugal mainland, Azores and Madeira Currently IM is collecting data in real-time (low latency) from 4 tide gauge stations in Portugal Mainland and the Ponta Delgada station (Azores) (a GLOSS station operated also by IH) is received at IM trough the GTS communication system with an average latency of 2.5 minutes

Tsunami Analysis Tool

With The TAT it is possible to compare in real time the sea level observations and the tsunami waveforms for the selected scenario ; With this procedure it is possible to update the messages issued for the civil protection

What is missing?

No offshore stations are in place and these are essential for tsunami detection before it hits the coast. The shortest tsunami travel times to coastal points in the Gulf of Cadiz are rather short, 20-30 minutes, and this shows the utmost importance of deploying tsunami sea bottom stations.

3 Tsunameters (red dots) 100 km apart

Summary

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The backbone of the PtTWS is in place

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Basic functionalities are installed at I.Meteorologia

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Offshore stations are missing

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Funding is a problem

NEAM REGIONAL WATCH CENTERS NETWORK

Portugal – RTWC FRANCE ITALY PORTUGAL GREECE North-Eastern Atlantic Western Mediterranean Central Mediterranean TURKEY