(1) NWPTA information is issued when NWPTAC detects an earthquake of magnitude 6.5 or more in its Monitoring Area, which covers the North-western Pacific and a portion of its South-western part as well as the South China Sea region.

(2) NWPTAC forecasts the tsunami and issues products for its AoS (see Figure).

(3) Data from tsunami observation reports received by NWPTAC are included in subsequent NWPTA messages as necessary.

(4) If the Centroid Moment Tensor (CMT) solution becomes available after the above NWPTA is issued, NWPTA based on real-time simulation are provided.

NWPTAs are provided via the GTS with the heading of WEPA40 RJTD and by e-mail and fax. Users are strongly advised to adopt multiple communication channels in order to ensure receipt.

Tsunamigenic potential is evaluated from earthquake magnitude as follows:

No tsunamigenic potential is associated with earthquakes occurring inland or at depths of 100 km or more.

A tsunami amplitude and an arrival time are estimated for each FP in coastal areas (See Figure and Table). This information is listed in NWPTA messages with the names of FPs and their latitudes/longitudes (to the nearest 0.1 degrees) in coastal-block groups.

Amplitude here is defined as the maximum distance between the crests of tsunami waves and the undisturbed sea level. Estimated tsunami amplitude is indicated only for FPs where tsunami of 0.3 m or more is expected to reach. The classifications are 0.3 - 1 m, 1 - 3 m, 3 - 5 m, 5 - 10 m and over 10 m. When tsunami amplitude of less than 0.3 m is estimated for all FPs, NWPTA message states “Estimation at forecast points - no tsunami waves with an amplitude of 0.3 meters or more are expected at any forecast point.”

(4) Tsunami Observation

Information on the amplitude of the largest wave (to the nearest 0.1 m) and other data on tsunami waves observed at tidal stations with telemetric links to NWPTAC are provided as necessary.