Geological aspects of the Tonga earthquake, 23 June 1977

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Paterson, B.R. 1977 Geological aspects of the Tonga earthquake, 23 June 1977. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 297 20 p.

Abstract: The Tonga earthquake of 23 June 1977 caused considerable damage to buildings on the main islands of ‘Eua and Tongatapu. The extent of the damage which was surprisingly severe for and epi-central distance of 230 km, was largely the result of a low standard of construction and the absence of and earthquake resistant design. On Tongatapu damage was confined mainly to larger buildings, particularly primary school buildings of a standard concrete block design. On ‘Eua where felt intensities were slightly higher, numerous dwellings either collapsed or were severely damaged. On both islands the buildings most severely damaged were those constructed of concrete blocks. As the near surface geology does not account for the difference in damage between the two islands; it is concluded that the overall shape of the islands was the main contributing factor. The Kingdom of Tonga is located in a seismically active belt in which earthquakes of at least the magnitude of the recent one can be expected on average every 13 years. To protect lives and property it is essential that a code of building standards be introduced and enforced throughout the islands with particular emphasis on buildings of masonry construction. It was entirely fortuitous that no lives were lost during the last earthquake and in a situation where the population have low earning capacity and no comprehensive insurance against natural disasters, the raising of building standards would be sound policy. (auth)