Rupture process of the 2020 Mw = 6.9 Samos, Greece earthquake on a segmented fault system constrained from seismic, geodetic, and tsunami observations

Abstract

The seismic, geodetic, and tsunami observations are utilized to investigate the October 30th 2020 Samos, Greece earthquake. We adopt back projection (BP) and multi-point source (MPS) techniques to determine the rupture directivity and focal mechanism change of this event. Both methods reveal a unilateral rupture propagation to the west of the epicenter, and also resolve a changed focal mechanism. We use a two-segment-faults geometry to parameterize the fault model with strikes at 283° for the east segment and 250° for the west respectively, and conduct a finite fault inversion (FFI) combining seismic and geodetic observations. The kinematics results indicate the whole rupture process lasts about 25 s, yielding a total seismic moment of 3.16×1019 Nm (Mw = 6.9) with a peak moment rate reaching 3.1×1018 Nm/s around 10 s. The rupture is composed of two asperities separated by the junction of two fault planes. The main slip area, with maximum amplitude reaching three meters, distributes at a shallow depth and displays a complementary pattern with aftershocks. The slip in the first six seconds is dominated by a pure normal faulting mechanism, while the following rupture includes an additional strike-slip component. The change of focal mechanism reflects the tectonic transition from dilatation to lateral shearing, which is also evident in the aftershock mechanisms. The synthetic tsunami waves also well fit three tidal gauge observations. The coseismic Coulomb stress is calculated to analyze the relationship between the mainshock and aftershock evolution. The mechanism combination of two rupture epochs reflects the combination of shear and dilatational stress status and complicated fault system of the Samos source area.