We use optical satellite data to map the co-seismic displacements for the Mw=7.5 strike-slip earthquake of 28 September 2018 in Palu, Sulawesi, Indonesia. This was a strike-slip faulting event at shallow depth that occurred within the interior of the Molucca Sea microplate, which is part of the Sunda tectonic plate. Using optical image correlation from Sentinel-2 and Planet imagery, we mapped the surface rupture extent of the earthquake and calculated the co-seismic offsets. Before- and after- the earthquake image acquisitions were analyzed using MicMac software and the MPIC-OPT service on the ESA Geohazards TEP platform. Our results include the mapping of a) the detailed trace of the ruptured fault at the southern part of the region (Palu segment) and b) a more complex deformation pattern at the northern part of the rupture. Analysis of the horizontal displacement field and sequential profiles across the fault also enabled mapping of the fault zone complexity, secondary faulting, fault zone width and large co-seismic gravitational phenomena. A mean displacement of 3-5 metres was calculated for a total earthquake rupture length of more than 140 km. Our results agree with the focal mechanism solution for the earthquake which indicates that the rupture occurred on a left-lateral, north-south striking fault. The significance of this event is also associated with the severity of the tsunami impact attributed to a strike slip fault. Further investigation is necessary to determine the source of the tsunami as primarily tectonic or due to another mechanism although a more complex mechanism is likely.

Report submitted to EMSC on 19 October 2018 12:00 UTC