We investigated rupture geometry, size, and slip distribution of October 30, 2020, Samos (Sisam)-Kusadasi earthquake combining seismographs, GPS measurements, and SAR analysis. Right after the earthquake, we measured 13 additional campaign-based GPS sites to intensify the available GPS network consisting of 10 continuous stations. We combined all available seismographs to have the best possible accuracy for mainshock and aftershock hypocenter locations. We compiled all available seismic profiles and integrated them using high-resolution bathymetry to map seismically active faults. The mainshock hypocenter is located at 37.913 +/- 0.009 N degrees and 26.768 +/- 0.017 E degrees and a depth of 12.3 +/- 1.7 km. Our fault plane solution shows that the mainshock has almost a pure normal-type mechanism. Based on accurate aftershock locations as well as InSAR results, the mainshock rupture is subsegmented with two north-dipping rupture planes. The rupture probably starts on a low angle plane generating 1.1 m average slip between the depths of 9-14 km. It merges to a steep plane at 9 km depth where it generates 1.2 m average slip extending towards the surface near the shoreline of Samos (Sisam) Island. Total size of the two rupture planes and their average slips determine that the magnitude of the mainshock is (M-w) 6.92 +/- 0.02. The mainshock has substantially increased Coulomb stress on several fault segments near the towns Kusadasa and Soke, which have the potentials to generate strong earthquakes. It also nonnegligibly increased Coulomb stress on several fault segments south of Izmir giving a warning for increased earthquake hazard in this highly inhabited area.