Ghasemi H.,Geoscience Australia |
McKee C.,Port Moresby Geophysical Observatory |
Leonard M.,Geoscience Australia |
Cummins P.,Geoscience Australia |
And 5 more authors.
Natural Hazards | Year: 2016
We developed a probabilistic seismic hazard map of Papua New Guinea expressed in terms of peak ground acceleration with return period of 475 years. The calculations were performed for bedrock site conditions (Vs30 = 760 m/s). A logic-tree framework was applied to include epistemic uncertainty in the seismic source as well as ground motion modelling processes. Two seismic source models were developed using area source zones and smoothed seismicity, respectively. Based on available geological and seismological data, defined seismic sources were classified into four different tectonic environments. For each of the tectonic regimes three ground motion prediction equations were selected and used to estimate the ground motions at a grid of sites with spacing of 0.1° in latitude and longitude. Results show a high level of hazard in the coastal areas of Huon Peninsula and New Britain–Bougainville regions and a relatively low level of hazard in the southwestern part of Papua New Guinea. Seismic hazard disaggregation results show that in the Huon Peninsula region high seismic hazard is caused by modelled frequent moderate to large earthquakes occurring on the Ramu-Markham Fault Zone. In the New Britain–Bougainville region the distance to the subduction zone associated with the New Britain Trench mainly controls the calculated level of hazard. It is also shown that the estimated level of peak ground acceleration is very sensitive to the selection of ground motion prediction equations. Overall our results differ significantly from those of previous studies, and we surmise that these differences are due to our use of modern ground motion prediction equations and earthquake source information. © 2016 Crown Copyright as represented by: the Commonwealth of Australia (Geoscience Australia) 2016
McKee C.O.,Port Moresby Geophysical Observatory |
Baillie M.G.,Queen's University of Belfast |
Reimer P.J.,Queen's University of Belfast
Bulletin of Volcanology | Year: 2015
The most recent major eruption at Rabaul was one of the largest known volcanic events at this complex system, having a volcanic explosivity index (VEI) rating of 6. The eruption generated widespread pumice lapilli and ash fall deposits and ignimbrites of different types. The total volume of pyroclastic material produced in the eruption exceeded 11 km3 and led to a new phase of collapse within Rabaul Caldera. Initial 14C dating of the event yielded an age of about 1400 years bp, and the eruption became known as the “1400 bp” eruption. Previous analyses of the timing of the eruption have sought to link it to events in ad 536 and ad 639. However, we have re-evaluated the age of the eruption using the Bayesian wiggle-match radiocarbon dating method, and the eruption is now thought to have occurred in the interval ad 667–699. The only significant equatorial eruptions recorded in both Greenland and Antarctic ice during this interval are at ad 681 and ad 684, dates that coincide with frost rings in bristlecone pines of western USA in the same years. Definitively linking the Rabaul eruption to this narrow age range will require identification of Rabaul tephra in the ice records. However, it is proposed that a new working hypothesis for the timing of the most recent major eruption at Rabaul is that it occurred in the interval ad 681–684. © 2015, Springer-Verlag Berlin Heidelberg.
McKee C.O.,Port Moresby Geophysical Observatory
Bulletin of Volcanology | Year: 2015
A major, geologically youthful, submarine caldera volcano, Tavui, was discovered in the Rabaul area of Papua New Guinea in 1986. Tavui Volcano has lateral dimensions of 9 to 10 km, slightly smaller than those of Rabaul Volcano, but Tavui’s caldera is much deeper than the nested caldera complex at Rabaul, and in general, its escarpment walls are very steep. The two caldera systems are essentially silicic and are separated by a zone of dominantly basalt-andesite stratovolcanoes. Rock samples dredged from Tavui have low- to medium-K contents, in contrast to the medium- to high-K rocks of Rabaul, indicating that the two systems have evolved separately and that the chemical, and perhaps physical, conditions within these neighbouring systems are different. Tavui is the likely source of the 6.9 ka BP Raluan Ignimbrite, the penultimate major eruption deposit in the Rabaul area. The Raluan Ignimbrite is rhyolitic and has geochemical characteristics incompatible with those of products from Rabaul Volcano. On the other hand, there is a close match between the geochemistry of the Raluan Ignimbrite and that of rhyolitic samples dredged from Tavui Caldera. The much older (≈79 ka) Tokudukudu Ignimbrite, which is also rhyolitic, is slightly more K-rich than both the Raluan Ignimbrite and rhyolites dredged from Tavui Caldera, but in general, its geochemical characteristics are similar to those of Tavui rhyolites and, therefore, is considered to be a possible product of Tavui. The recognition that Tavui was the likely source of the penultimate major eruption and of at least one other significant eruption in the Rabaul area markedly changes the perceptions of local volcanic hazard. In addition, Tavui’s potential for generation of tsunami is acknowledged, not just in association with volcanic eruptions but also from earthquake-related and possibly spontaneous collapse of parts of the steep caldera walls. The presence of Tavui greatly increases the net geologic hazard in the Rabaul area. © 2015, Springer-Verlag Berlin Heidelberg.