Japanese
Home > For NMHSs > NWPTAC > NWPTAC General

NWPTAC top NWPTAC general information NWPTAC Forecast Points NWPTA template NWPTAC communication test NWPTAC technical description NWPTAC site map


GEOGRAPHICAL COVERAGE, TIMING AND CRITERIA FOR ISSUANCE


(1) A Northwest Pacific Tsunami Advisory (NWPTA) is issued when NWPTAC detects an earthquake of magnitude 6.5 or greater in its area of responsibility (see the Figure), which includes the northwestern Pacific, part of the southwestern Pacific, and (on an interim basis) the South China Sea region.

(2) When the NWPTAC receives reports of tsunami observations, the tsunami observational data are presented in subsequent NWPTA messages as required.

(3) When the location and magnitude of the earthquake are re-estimated using seismic data subsequently obtained and/or an unexpectedly significant tsunami is observed, further NWPTA is issued to revise the previous advisory.



MEANS OF DISSEMINATION


NWPTAs are provided via the GTS with the heading of WEPA40 RJTD, by e-mail and by facsimile. Recipients are strongly encouraged to use multiple means of communication in order to ensure receipt.



CONTENTS OF THE ADVISORY


The NWPTA contains: (1) earthquake information; (2) tsunamigenic potential; (3) the estimated amplitude and arrival time of the tsunami; and (4) observations of the tsunami. The dates and times used in the NWPTA are given in Universal Time Coordinated (UTC) format. The earthquake parameters of the NWPTA are coordinated and consistent with those of the PTWC bulletin. The template and sample messages of the NWPTA are presented in the Template page.


(1) Earthquake information

a. Origin time
b. Coordinates (latitude and longitude) of the epicenter
c. Location (name of geographical area)
d. Depth (only for earthquakes at a depth of 100 km or more)
e. Magnitude (i.e. moment magnitude. If the value given is JMA magnitude
(Mjma),(MJMA) is specified - see the JMA part of the annexes.)


(2) Tsunamigenic potential

Tsunamigenic potential is evaluated according to the magnitude of the earthquake as follows:

M>7.8

Possibility of a destructive ocean-wide tsunami

7.8≥M>7.5
Possibility of a destructive regional tsunami within 1,000 km of the epicenter
7.5≥M>7.0
Possibility of a destructive local tsunami within 100 km of the epicenter
7.0≥M≥6.5
Very small possibility of a destructive local tsunami

No tsunamigenic potential is evaluated for earthquakes occurring in inland areas or at a depth of 100 km or more.


(3) Estimated amplitude and arrival time of tsunami

The tsunami amplitude and arrival time are estimated for each forecast point in coastal areas (See Figure and Table). These estimated values are listed in the NWPTA messages with the names of the forecast points and their latitude and longitude (to the nearest tenth of a degree), in groups of coastal blocks.

‘Amplitude’ is defined as the greatest difference between the crest of a tsunami wave and the undisturbed sea level. The estimated tsunami amplitude is indicated only for forecast points that a tsunami of 0.5 m or greater is expected to reach(†). Tsunami amplitude is classified in categories of 0.5m, 1m, 2m, 3m, 4m, 6m, 8m and over 10m. When a tsunami amplitude of less than 0.5 m is estimated for all the forecast points, the message “ESTIMATION AT THE FORECAST POINTS - NO TSUNAMIS WITH AMPLITUDE OF 0.5 METER OR OVER ARE EXPECTED AT ANY OF THEM” is stated in the NWPTA.

(†) See Technical Description page, if you want to know the technical information.



(4) Observations of tsunami

When tsunami waves are actually recorded at tidal stations that are telemetrically linked to the NWPTAC, these observational data are provided as necessary, including the amplitude of the largest wave to the nearest 0.1 m unit (in this case, ‘amplitude’ refers to half the vertical length from the trough to the crest of the wave).