Source Characteristics of Destructive Earthquakes with Mw ≥ 7.5 Occurred During 2017-2018.

In recent years many devastating earthquakes with Mw ≥ 7.5 occurred during 2017-2018 asa result of active plate interactions near the major mega-thrust subduction zones. Theyreveal tectonic complexities and astonishing deformation styles associated with theplate movements. In this study, we determined source mechanism parameters andfinite-fault slip distribution models of four destructive earthquakes (Mw ≥ 7.5) byperforming point-source and finite-fault slip inversions. The shapes and amplitudesof long-period and broad-band P- and SH-waveforms recorded by the Federationof Digital Seismograph Networks (FDSN) and the Global Digital SeismographNetwork (GDSN) stations in the distance range of 30˚ - 90˚ are compared withsynthetic waveforms. Finite-fault slip models of earthquakes are estimated by applyinga hybrid back-projection method that uses teleseismic P-waveforms to integratethe direct P-phase with reflected phases from structural discontinuities near thesource. Overall results indicate various faulting mechanisms at relatively shallowfocal depths (h<70 km). For example, the February 25, 2018 Papua New Guinea(Mw: 7.5) earthquake indicates a thrust faulting mechanism associated with theconvergence of Australia and Pacific Plates. The September 28, 2018 Sulawesi (Indonesia)earthquake (Mw: 7.5), occurred within the Molucca Sea micro-plate at the eastern part ofIndonesia shows a strike-slip faulting mechanism reflecting the complex deformationsrelated to the interactions between Australia, Sunda, Pacific and Philippine Seaplates. Regardless strike-slip mechanism involved, this large earthquake producedunexpected tsunami waves along the coastal planes of Sulawesi. Finite-fault slipmodels reveal several heterogeneous rupture propagations and slip distributions onfault planes of those earthquakes. In addition, distributions of P- wave first motionpolarities recorded at near-field and regional seismic stations are consistent withthe best-fitting minimum misfit source mechanism solutions of earthquakes. Thisstudy is partially supported by the Turkish Academy of Sciences (TÜBA-GEBIP). [ABSTRACT FROM AUTHOR]