ANALYSIS OF THE 2018 MW 7.5 PAPUA NEW GUINEA EARTHQUAKE USING THE SUB-PIXEL OFFSET METHOD

Situated in between the Australian and Pacific Plate, the New Guinea Island experiences ~70mm/yr of convergence. On 25th February 2018, an M_w 7.5 earthquake struck the Southern Highlands of the Papuan Fold-and-Thrust Belt. More than 200 aftershocks with M_w 4 and greater were recorded in 4 months after the main shock. However, efforts to constrain the earthquake fault geometry and slip location has proven difficult due to the lack of a dense seismic and GPS network in this densely vegetated region. Here, we present the use of sub-pixel offset method on synthetic aperture radar (SAR) images as an alternative to providing near-field measurements of coseismic displacement. Although this method is limited by the pixel resolution of the images, SAR technique can image ground surface in all weather conditions and in day/night times. We used an ascending and descending path from the Sentinel-1 (S1) satellite to obtain a 3D coseismic deformation of the earthquake and to identify trigger landslides in the vicinity. With the S1 image resolution, we can measure surface displacement >0.5 m. Our coseismic measurements indicate ~40 km long surface rupture along the fold-and-thrust belt, and there are at least two fault segments involved with the earthquake. The peak displacement is ~3 meters for the fault at the eastern side. We also find several landslides on the hanging wall, which agrees with field investigation. We apply a finite fault inversion using the sub-pixel offset-based coseismic displacement to constrain the fault slip distribution. Our inversion result suggests a peak slip close to 3 meters. Our work shows the significance of using satellite geodesy methods for constraining an earthquake in areas lack of seismic and land-based GPS data.