Earthquakes in Tonga.

The largest earthquake, which has occurred in Tonga, was on 23 June 1977. This earthquake had a surface wave magnitude (Ms) of 7.2. It shook all the southern islands of the Kingdom. The tremor was also felt in Hafapai and Vavafu in the north. The earthquake was located approximately 200 kilometers to the southwest of Tongatapu (Kruger-Knuepfer et al., 1986). The earthquake caused damaged to houses, churches, wharfs and public utilities. The old Vuna Wharf in Nukufalofa was badly damaged and it has remained in that state up to the present. The Tonga Chronicle published pictures of damage to the wharf and various buildings.

The International Seismological Centre (ISC) hypo central data for this earthquake are as follows:

Time:      12h 08m 33.7s, 22 June, 1977 (UTC)

(00h 08m, 23 June 1977)

Location:              Longitude 175.74W, Latitudes 22.91S,

Depth:    69km

The epicentre was located about 190 km to the south west of Tongatapu and eEua.

Modified Mercalli scale of intensities of shaking ranged from MMVII and MMVIII on Eua to MMV1 and MMVII on Tongatapu to less than MMV on the northern island groups of Hafapai and Vavafu (Campbell et at, 1977). Considerable damage to structures resulted from this earthquake.

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Data source (Country report)

1.      Name: Rennie Jegsen VAIOMO' UNGA

2.      Organization: Assistant Geologist, Ministry of Lands, Survey and Natural Resources

3.      Course: 1998-1999 S

4.      Title: SEISMOLOGY WORKS IN TONGA.