Supershear rupture of the 28 September 2018 Palu earthquake inferred from Empirical Green's Function analysis

Abstract

We deconvolved 22 teleseismic waveforms of Mw6.1 earthquake with Mw7.5 Palu earthquake to obtain Apparent Source Time Functions (ASTFs). Analysis of those ASTFs resulted rupture directivity, rupture length and rupture velocity of the earthquake. The main earthquake ruptured to N 2270E direction along 80 km away from the epicenter at an average speed of 4.5 km/s. The rupture velocity which is greater than local shear-wave velocity of 3.5 km/s indicated supershear characteristic of the earthquake. An ASTF of SNZO station was used to infer 1-D slip distribution of this earthquake. Based on this ASTF we calculated earthquake moment of 1.45 x 1020 Nm that released in 30 seconds. The largest seismic moment released between 0-15 seconds and decreased before it stopped at 30 seconds. A Maximum slip of 8 meters occurred at a distance of 20 km to the south of the epicentre and decreased to around 4 meter near Palu City.