Abstract

The May 15, 1992, earthquake on the Huon Peninsula, Papua New Guinea, resulted in the uplift and large-scale mortality of intertidal fringing coral reefs. Reduction in the highest level of survival of intertidal massive corals was used as a proxy for assessing the amount of coseismic uplift over 45 km of the Huon coastline. Measurements were gathered from three sites one and three months after the earthquake. Sea-level pressure gauges in place in the northern end of Sialum Lagoon showed not uplift, but subsidence, from the earthquake. Uplift ranged from ∼7 to 13 cm, and subsidence ranged from 8 to 14 cm. The May 15, 1992, earthquake corroborates the coseismic origin of the raised reef terraces of the Huon Peninsula. Greater uplift of the land in the southeast relative to the northwest is consistent with the regional Quaternary uplift pattern. The close proximity of subsidence (shown by sea-level gauges) to uplift (shown by coral mortality) is a manifestation of the abundant fault blocks in the area. Uplift rates of 3.0-5.2 m/ka calculated from the earthquake are only marginally higher than previous estimates based on radiometric age dates and terrace geomorphology. The first directly observed earthquake uplift event on the Huon Peninsula has yielded only centimetre-scale coseismic uplift. Thus, individual Holocene and Pleistocene terraces thought to have been the result of metre-scale displacement from single earthquakes may rather have been due to successive episodes of centimetre-scale uplift on constructional reef platforms. The clustered history of earthquakes on the Huon Peninsula throughout the past 100 years indicates the complexity involved in assessment of seismic risk throughout the world.

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