The Papua New Guinea tsunamis from the 29 March and 5 May 2015 Mw 7.5 earthquake doublet

Abstract:

We characterized tsunamis from the 29 March and 5 May 2015 Kokopo, Papua New Guinea Mw 7.5 earthquake doublet by applying teleseismic body-wave inversion and tsunami simulation. These events are the first instrumentally-recorded tsunamis from the New Britain subduction zone. Seismic body-wave inversions using various rupture velocities (Vr) showed almost similar source-time functions and waveform agreements but the spatial distributions of the slips were different. In this study, the rupture velocities were reliably estimated from joint use of seismic and tsunami data for the earthquake doublet; and they (i.e., 1.75 and 1.5 km/s) were smaller than typical Vr values for tsunamigenic earthquakes. The largest slips on the fault were similar (2.1 m and 1.7 m), but the different depths and locations yielded maximum seafloor uplift of ~ 0.4 m and ~ 0.2 m, respectively, which resulted in different tsunami powers. This indicates that even though the earthquake size and rupture durations are similar for an earthquake doublet, the resultant tsunami would be different, depending on the location and depth of the earthquake source, as well as water depth around the source. Simulations of hypothetical tsunami scenarios with large magnitudes of Mw 8.4 and 8.5 from the New Britain subduction zone showed that the shoreline tide gauge zero-to-crest amplitude can reach up to 10 m in Rabaul. Most of the tsunami was confined within the Solomon Sea indicating low tsunami hazards for far-field destinations such as Australia and New Zealand in the south. For other regions, ocean submarine ridges and island chains can significantly reflect back tsunami waves and limit the far-field reach of tsunamis.