July 17 Papua New Guinea tsunami

Prof. Abe's Tsunami Magnitude

Dear tsunami scientists:

I tentatively estimated the tsunami magnitude Mt for the July 17 Papua New Guinea tsunami from tsunami wave amplitudes recorded in Japan.

1. Used formula

Mt = log H + B

H: Average of maximum tsunami amplitudes recorded in Japan

B: Constant which depends on each pair of source region and observation region

For the source region south of Japan, B = 8.4. This value has been obtained for the Guam and Mariana events and has not yet been published. (Cf. Abe, K., J. Geophys. Res., 84, 1561, 1979)

2. Data

Eleven data are available throughout Japan. H(average) = 0.13 meters +/- 0.03 meters

3. Result

Mt = 7.51

4. Remarks

USGS obtained Ms=7.0 from seismic surface waves. Mt is greater than Ms by 0.5. The PNG event is conseidered to be a tsunami earthquake that generates significantly large tsunamis but relatively weak seismic waves.

The Irian Jaya earthquake of February 17, 1996, set off a large tsunami at Biak Island in New Guinea Island. Mt and Ms of this event are 8.0 and 8.0, respectively.

Today (July 20, Monday) is Marine Day, a national holiday created two years ago to celebrate the endowments of the ocean and wish for the continued prosperity of Japan, a maritime country.

Yours sincerely,
Katsuyuki Abe
July 20, 1998

SISSANO, PAPUA NEW GUINEA, 20-JUL-1998: A man salvages possessions from the ruins of his house in Sissano July 20 in the remote North West of Papua New Guinea. Rescue workers believe that up to 3,000 people were swept to their deaths when three giant tidal waves struck July 17 and devastated seven coastal towns. [Photo by Torsten Blackwood, AFP]

SIMMANO, PAPUA NEW GUINEA, 20-JUL-1998: Over view of the Simmano lagoon on the northwest coast of Papua New Guinea shows the devastation July 20 were some 3,000 people are feared dead after three giant tidal waves struck July 17 after an underwater earthquake. The waves destroyed seven coastal towns. [Photo by AFP]

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