A new approach to monitoring stochastic features of earthquake series was applied to track the preparatory process of the 2017 Tehuantepec, Mexico, Mw8.4 earthquake. The seismicity was parameterized by elapsed times and epicentral distances from the directly preceding earthquakes and by earthquake magnitudes. The transformation to equivalent dimensions ensured the comparability of these parameters. We were calculating the average distance between earthquakes in the transformed parameter space in moving in time data windows, each consisting of 100 events. The average distance exhibited a consistent upward trend from ten to two years before the main shock. Then, it declined until the main shock. This precursory up-down signal was highly significant statistically. We showed that the detected time changes of the average distance resulted from the evolution of the earthquake clustering in the considered parameters' equivalent dimensions space.

On 20 July 2017, an Mw6.6 earthquake occurred offshore Kos Island, the largest to occur in the affected area in the instrumental era, and in the past 60 years in the southeastern Aegean Sea. We estimated the aftershocks relative locations by applying the double-difference technique using both differential times from phase-picked data and waveform cross-correlation. The relocated aftershocks are clustered at least in three distinctive patches, creating a zone getting a total length of about 40 km, elongated in a nearly east-west direction, mainly concentrated at depths 8–15 km, with the mainshock hypocenter placed at ~13 km, implying a seismogenic layer of 7 km thickness, indicative for normal faulting earthquakes with Mmax~6.5. The aftershock fault plane solutions are predominantly suggestive of normal faulting in response to the north-south extension of the back-arc Aegean area. We further applied the satellite radar interferometry (InSAR) technique to define the coseismic surface displacements. This field of deformation along with the available vectors of displacement measured by the Global Navigation Satellite System (GNSS) technique was combined with the seismological data to determine the rupture geometry and process, with the coseismic slip ranging between 0.5 and 2.3 m. The peak moment release occurred in the depth interval of 9–11 km, consistent with the depth distribution of seismicity in the study area. We used the variable slip model to calculate Coulomb stress changes and investigate possible triggering due to stress transfer to the nearby fault segments.

The potentiality of an improved physics-based earthquake simulation algorithm for modelling the long-term spatiotemporal process of strong earthquakes preparation is explored. The physical model on which this version of our simulation algorithm is based includes the Rate & State constitutive law, in addition to tectonic stress loading and static stress transfer. We applied the simulator code to a physical model of the Corinth Gulf (Greece) fault system, a rapidly extending rift about 100 km long, where the deformation is taken by major fault segments aligned along the southern coastline of the Corinth Gulf, and associated with several strong (6.0) earthquakes in the last few centuries. In particular, the recurrence time of strong events and their spatial relation are studied. The results of this simulation provide interesting inferences on the spatiotemporal properties of seismic activity in the study area. As the simulator algorithm allows displaying the stress pattern on all the single elements constituting the seismic structure, in this study we have focused our attention on the time evolution of the level of stress before, during and after strong earthquakes. In particular, we have quantitatively recognized that the ratio between the average stress and its standard deviation on the patches constituting a specific fault segment, always increases at an accelerating rate before a large rupture on a part or the entire segment, or even several collective segments.