Large Shallow Slip Along the Palu-Koro Fault Associated with Supershear Rupture

The 2018 Palu earthquake was a stunning example of a major strike-slip faulting event that generated severe ground shaking and liquefaction, as well as a local tsunami. Using a combination of remote sensing and seismic data, we show that the central portion of the rupture reached the surface with little to no shallow slip deficit and propagated at supershear velocity.

We use radar and optical remote sensing data from three satellites (ALOS-2, Sentinel-2 and Landsat-8) to derive a detailed map of surface displacements along the rupture, and show that along the central segment the earthquake generated a relatively constant 5 to 6 meters of slip at shallow depths. We find that the maximum slip along this segment occurred at the surface and slip was focused within the top few km of the fault, opposite to the pattern seen during other moderate to large strike-slip events. We use teleseismic back-projection to show that the rupture also propagated at supershear velocity along this central segment. To the north and south, the initiating and terminating fault segments either did not break the surface or had a significant shallow slip deficit, despite similar peak slip at depth.

Taken together, these results demonstrate that a highly energetic rupture can overcome the mechanisms leading to the shallow slip deficit commonly observed on strike-slip faults (e.g. Kaneko & Fialko, 2011). Such events may occur infrequently, but as in the case of Palu, likely lead to strong ground motion due to the proximity of large slip to the free surface. Thus, this scenario represents a significant and potentially un-modeled hazard for other communities on or near major faults