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The 30 October 2020 Samos earthquake (Mw 7.0) ruptured an east–west striking, north dipping normal fault located offshore the northern coast of Samos Island, previously inferred from the bathymetry and regional tectonics. This fault, reported in the fault-databases as the North Samos and/or Kaystrios Fault, ruptured with almost pure dip-slip motion, in a region where both active extension and strike-slip deformation coexist. Historical information for the area confirms that similar ~ Mw7 events had also occurred in the broader Samos area, though none of the recent (last ~ 300 years) mainshocks appears to have ruptured the same fault. The spatial and temporal distribution of relocated aftershocks indicates triggering of nearby strike-slip and normal fault segments, situated in the areas where static stress has increased due to the mainshock generation. The relocated aftershocks and the slip model indicate that the sequence ruptured the upper crust (mainly the depth range 3–15 km). The top of the rupture plane nearly reached the sea bottom, located at a depth of

We combine probabilistic and deterministic approaches in an attempt to tackle a challenging topic in engineering seismology, that of the prediction of strong ground motion in urban areas located close to active faults, with sparse modern seismicity. The case we study is the city of Xanthi in northern Greece and we generate bedrock synthetic time series to be used as input motions into site-specific site effect analysis. We re-assess the seismic hazard using the probabilistic method and then perform hazard deaggregation in order to define realistic earthquake scenarios, which we examine in a deterministic way. The scenarios examined are: (a) a reference earthquake of M6.7, return period 100 years and at ~30 km distance from the city and (b) a reference earthquake of M5.8, return period 475 years and at ~3 km distance from the city of Xanthi. To compute synthetic time series for the distant source, we apply the stochastic method for finite faults. For the near-fault earthquake scenario we adopt a hybrid deterministic-stochastic approach that includes the semi-analytical method implemented in the COMPSYN code for the low frequency (~ 3 Hz). The results of the probabilistic and the deterministic approaches converge to a satisfactory degree.

The densely populated city of Thessaloniki (Northern Greece) is situated in the vicinity of active seismic faults, capable of producing moderate to strong earthquakes. The city has been severely affected by such events several times during the last 15 centu- ries. The most recent event occurred on 20 June 1978 (M6.5) in the Mygdonian graben, with an epicentral distance of about 30 km, causing extended damage in the city, with macroseismic intensities between MSK V+ and VIII+. The majority of buildings affected by the earthquake were of reinforced-concrete typology, typical to many southern European metropolitan areas. The source properties of the normal-faulting causative event and the source-to-city propaga- tion path are well known from previous studies. The soil structure under the metropolitan area of Thessaloniki is assigned NEHRP categories B, C, D on the basis of geotechnical and geologic information and single-station ambient-noise measurements. A finite source model and various rupture scenarios of the June 1978 earthquake are used to perform forward sto- chastic modeling of strong ground motion in terms of peak ground and spectral acceleration. Rock motion is assessed under the city and it is transferred to the surface in accordance with the respective soil category. A GIS tool is employed to compare the estimated strong-motion parameters with the observed detailed damage pattern induced by the 1978 earthquake. For selected natural periods, a satisfactory correlation is established between macroseismic inten- sity and peak ground and spectral acceleration, thus encouraging the application of stochastic modeling for generating realistic ground-shaking scenarios in metropolitan areas.