Tectonic geomorphology and Holocene uplift rates of the Lae Urban Area, Papua New Guinea

Updated: 2026-05-13

Lae is Papua New Guinea’s (PNG’s) second largest city and is the home of PNG’s largest port. Here, a convergence rate of ~50 mm/yr between the South Bismarck Plate and the Australian Plate is accommodated across the Ramu-Markham Fault Zone (RMFZ). The active structures of the RMFZ bifurcate immediately west of the Lae urban area, with one trace (the Wongat South Thrust) trending southeast through Lae City and connecting to the Markham Trench within the Huon Gulf. The geomorphology of the Lae urban area relates to the interaction between riverine (and limited marine) deposition and erosion, and range-building over the Wongat South Thrust. Flights of deformed river terraces imply repeated tectonic uplift events. Terrace riser heights are typically on the order of 2.5-3.0 m, indicating causative earthquake events of greater than magnitude 7.0. Preliminary dating of fluvial and marine terrace deposits indicates a recurrence for these events in the order of 300-400 years, at an uplift rate of ~12 m/kyr. The results of the tectonic geomorphology study form part of a PNGAus partnership project, and will inform future seismic hazard and risk assessments for the region