The plate boundary between the Pacific-Caroline and Australian plates in northwestern New Guinea is associated with a geographic concentration of earthquakes developed in the Ransiki region of the northeastern Bird's Head Peninsula (West Papua, northwestern New Guinea) at the intersection of the Ransiki and Yapen faults. We examine these earthquakes based on regional geomorphological and lithostratigraphical frameworks, field observations of surface ruptures and liquefaction phenomena, and focal mechanisms of historical earthquakes. The Ransiki earthquakes are a set of 29 earthquakes from the Global Centroid Moment Tensor catalogue in the period 1977–2019 (magnitudes of Mw4.9 to Mw7.5). In the east, focal mechanisms show sinistral movement along the east-west trending Yapen Fault including the Mw6.7 earthquake on 21 April 2012. The largest earthquake was on 10 October 2002 (Mw7.5) and along with other earthquakes mainly in the southwest were associated with dextral movement indi
This thesis aims to establish how the late Cenozoic oblique convergence of the Pacific- Caroline and Australian plates has affected the tectonic history of the eastern Bird’s Head Peninsula in northwestern New Guinea. Emphasis is placed on insights provided by >5 magnitude earthquakes since 1976 and the structural geology of Miocene-Pleistocene sediments in the Manokwari area and Permian to Paleogene units of the northern Lengguru Fold Belt around Mawi Bay. The Bird's Head Peninsula is moving west- southwest relative to the Australian Plate based on GPS data, but slower than the west- southwest movement of the Pacific-Caroline Plate. This accounts for plate convergence between the Pacific-Caroline Plate and the Bird's Head Peninsula consistent with earthquakes caused by gently south dipping thrusts in an arc along the northern Bird’s Head coastline and indicating subduction along the Manokwari Trough. Southwards subduction along the New Guinea Trench to the northeast o