Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

The elevation of high-level terraces relative to the lower terraces (and marine terraces) may be used to constrain total uplift of these terraces since the time of their formation. Fluvial sandy gravel samples fromvarious surfaces were taken fromshallowhand- excavatedpits for OSL dating (Figs. 2 & 3). Dating of these samples will help constrain the timing of past earthquakes and associated recurrence intervals. D I S C U S S I O N The relationship of uplifted and folded surfaces to the underlying fault is conceptualised in the composite section presented in Fig. 4. It is clear from this model that the total uplift (and per earthquake event) will vary depending upon proximity to the fault; total uplift diminishes over several kilometres to the east. Furthermore, it should be noted that the total vertical displacement at a site comprises a component related to far field uplift across the fault, and a near field component of folding. As yet, we have not received the results of the OSL dating of our samples collected from fluvial terraces. However, radiocarbon dates obtained on corals (Buleka et al., 1999; Crook, 1989a; Liu, 1993) indicate that there has been ~ 4-5 m of uplift at Voco Point in the last ~ 1000 years (Crook, 1989a; Liu, 1993) suggesting 8-10 m of vertical displacement at the fault. Assuming a fault dip of 30°, a slip rate of 16-20 mm/a is possible; almost one-third of the contemporary convergence across the plate boundary. Fig. 2: Lae urban area with terrace treads related to the Bumbu and Busu Rivers marked. Channel-forms are labelled (e,g, Ch1 - Ch3). Anticlines relating to the extension of the Atzera Range anticline are inferred from topographic profiles (e.g. Figure 5). The Ramu-Markham Fault (Wongat South Thrust) may surface rupture northwest of the Lae Showgrounds, but expresses as a fold further east. Terrace elevation with age cartoon in the inset is schematic, and assumes (perhaps implausibly) all terrace elevations are tectonic. Relative heights of terrace risers are labelled with subscript ‘r’.