Raz de marée ?

(image d'un précédent séisme- celui d'aujourd'hui est parti plus au sud du Chili)

Tremblement de terre au Chili magnitude 8,8. L'onde se propage sur le Pacifique (durée en h)

Rappel: L'échelle de Richter est logarithmique de base 10: elle mesure le logarithme de l'énergie libérée.

Ne pas confondre Magnitude (M), Energie (E), et Intensité (I):

les formules sont, pour l'échelle de Richter:

Energie libérée: log(E) = 11,4 + 1,5 M (où log est le logarithme décimal, comme en chimie pour le pH: c'est-à-dire log(x) = ln(x) / ln10

Intensité I = Io.10^M où Io est l'intensité de référence.

Donc, entre 2 séismes de magnitudes M1 et M2 on a:

Pour l'énergie: log(E2) -log(E1) = 1,5 (M2 - M1) d'où E2 / E1 = 10^[ 1,5( M2 - M1)]

Pour l'intensité: I2 / I1 = 10^(M2-M1)

Ainsi, un tremblement de terre enregistrant 8,8 sur l'échelle de Richter transporte
10^[1,5( 8,8 - 7,8)] = 30 fois plus d'énergie qu'un de 7,8.

Entre celui-ci (mag 8,8) et celui d'Haïti (mag 7), l'énergie libérée est: 10^[ 1, 5 ( 8,8 - 7)] = 500 fois plus importante.

C'est le 5e plus fort tremblement de terre depuis 1900.


Déplacement de l'onde:

Chili-Marquises: 6800 km
Chili-Raiatea: 7500 km donc 700 km de plus, donc environ 1h de décalage par rapport aux Marquises si l'onde voyage à 700 km/h.




Pour plus d'info: site de la NOAA Pacific Tsunami Warning Center

dont voici le bulletin:

TSUNAMI BULLETIN NUMBER 014
PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS
ISSUED AT 1934Z 27 FEB 2010

THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC
OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA...
WASHINGTON...OREGON AND CALIFORNIA.

... A WIDESPREAD TSUNAMI WARNING IS IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

CHILE / PERU / ECUADOR / COLOMBIA / ANTARCTICA / PANAMA /
COSTA RICA / NICARAGUA / PITCAIRN / HONDURAS / EL SALVADOR /
GUATEMALA / FR. POLYNESIA / MEXICO / COOK ISLANDS / KIRIBATI /
KERMADEC IS / NIUE / NEW ZEALAND / TONGA / AMERICAN SAMOA /
SAMOA / JARVIS IS. / WALLIS-FUTUNA / TOKELAU / FIJI /
AUSTRALIA / HAWAII / PALMYRA IS. / TUVALU / VANUATU /
HOWLAND-BAKER / NEW CALEDONIA / JOHNSTON IS. / SOLOMON IS. /
NAURU / MARSHALL IS. / MIDWAY IS. / KOSRAE / PAPUA NEW GUINEA /
POHNPEI / WAKE IS. / CHUUK / RUSSIA / MARCUS IS. / INDONESIA /
N. MARIANAS / GUAM / YAP / BELAU / JAPAN / PHILIPPINES /
CHINESE TAIPEI

THIS BULLETIN IS ISSUED AS ADVICE TO GOVERNMENT AGENCIES.  ONLY
NATIONAL AND LOCAL GOVERNMENT AGENCIES HAVE THE AUTHORITY TO MAKE
DECISIONS REGARDING THE OFFICIAL STATE OF ALERT IN THEIR AREA AND
ANY ACTIONS TO BE TAKEN IN RESPONSE.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME -  0634Z 27 FEB 2010
COORDINATES -  36.1 SOUTH   72.6 WEST
DEPTH       -   55 KM
LOCATION    -  NEAR COAST OF CENTRAL CHILE
MAGNITUDE   -  8.8

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY

GAUGE LOCATION        LAT   LON    TIME        AMPL         PER
-------------------  ----- ------  -----  ---------------  -----
CABO SAN LUCAS MX    22.9N 109.9W  1833Z   0.36M /  1.2FT  12MIN
DART TONGA 51426     23.0S 168.1W  1844Z   0.04M /  0.1FT  30MIN
HIVA OA MARQUESAS     9.8S 139.0W  1741Z   1.79M /  5.9FT  12MIN
PAPEETE TAHITI       17.5S 149.6W  1810Z   0.16M /  0.5FT  10MIN
NUKU HIVA MARQUESAS   8.9S 140.1W  1745Z   0.95M /  3.1FT  04MIN
MANZANILLO MX        19.1N 104.3W  1705Z   0.32M /  1.0FT  24MIN
DART MANZANILLO 434  16.0N 107.0W  1611Z   0.07M /  0.2FT  24MIN
ACAPULCO MX          16.8N  99.9W  1549Z   0.16M /  0.5FT  24MIN
RIKITEA PF           23.1S 134.9W  1559Z   0.15M /  0.5FT  22MIN
DART MARQUESAS 5140   8.5S 125.0W  1531Z   0.18M /  0.6FT  18MIN
BALTRA GALAPAGS EC    0.4S  90.3W  1452Z   0.35M /  1.2FT  14MIN
EASTER CL            27.2S 109.5W  1205Z   0.35M /  1.1FT  52MIN
ANCUD CL             41.9S  73.8W  0838Z   0.62M /  2.0FT  84MIN
CALLAO LA-PUNTA PE   12.1S  77.2W  1029Z   0.36M /  1.2FT  30MIN
ARICA CL             18.5S  70.3W  1008Z   0.94M /  3.1FT  42MIN
IQUIQUE CL           20.2S  70.1W  0907Z   0.28M /  0.9FT  68MIN
ANTOFAGASTA CL       23.2S  70.4W  0941Z   0.49M /  1.6FT  52MIN
DART LIMA 32412      18.0S  86.4W  0941Z   0.24M /  0.8FT  36MIN
CALDERA CL           27.1S  70.8W  0843Z   0.45M /  1.5FT  20MIN
TALCAHUANO CL        36.7S  73.4W  0653Z   2.34M /  7.7FT  88MIN
COQUIMBO CL          30.0S  71.3W  0852Z   1.32M /  4.3FT  30MIN
CORRAL CL            39.9S  73.4W  0739Z   0.90M /  2.9FT  16MIN
SAN FELIX CL         26.3S  80.1W  0815Z   0.53M /  1.7FT  08MIN
VALPARAISO CL        33.0S  71.6W  0708Z   1.29M /  4.2FT  20MIN

LAT  - LATITUDE (N-NORTH, S-SOUTH)
LON  - LONGITUDE (E-EAST, W-WEST)
TIME - TIME OF THE MEASUREMENT (Z IS UTC IS GREENWICH TIME)
AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL.
IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT.
VALUES ARE GIVEN IN BOTH METERS(M) AND FEET(FT).
PER  - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.

EVALUATION

SEA LEVEL READINGS CONFIRM THAT A TSUNAMI HAS BEEN GENERATED
WHICH COULD CAUSE WIDESPREAD DAMAGE. AUTHORITIES SHOULD TAKE
APPROPRIATE ACTION IN RESPONSE TO THIS THREAT. THIS CENTER WILL
CONTINUE TO MONITOR SEA LEVEL DATA TO DETERMINE THE EXTENT AND
SEVERITY OF THE THREAT.

A TSUNAMI IS A SERIES OF WAVES AND THE FIRST WAVE MAY NOT BE THE
LARGEST. TSUNAMI WAVE HEIGHTS CANNOT BE PREDICTED AND CAN VARY
SIGNIFICANTLY ALONG A COAST DUE TO LOCAL EFFECTS. THE TIME FROM
ONE TSUNAMI WAVE TO THE NEXT CAN BE FIVE MINUTES TO AN HOUR, AND
THE THREAT CAN CONTINUE FOR MANY HOURS AS MULTIPLE WAVES ARRIVE.

FOR ALL AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS
AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT
OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME
THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN
CONTINUE FOR SEVERAL HOURS DUE TO RAPID CURRENTS. AS LOCAL
CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE
ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES.

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT.
THE TSUNAMI WARNING WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.

THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS
FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA.

.