Simulation of seismic triggering and failure time perturbations associated with the 30 October 2020 Samos earthquake (Mw 7.0)

The 30 October 2020 Samos earthquake (Mw = 7.0) ruptured a north-dipping offshore normal fault north of the Samos Island with an extensional mechanism. Aftershocks mainly occurred at the western and eastern ends of the rupture plane in agreement with the Coulomb static stress changes. Mechanism of aftershocks located west of the rupture supported activation of the neighboring strike-slip fault almost instantly. In addition, a seismic cluster including events with Mw similar to 4 has emerged two days later at the SE side of Samos Island. This off-plane cluster displays a clear example of delayed seismic triggering at nearby active faults. In this study, numerical simulations are conducted to mimic the instant and delayed seismic triggering observed after this event and evaluate resultant seismic cycle perturbations at adjacent faults and near Izmir, where amplified ground motions caused heavy damage. For this purpose, Coulomb static stress changes and seismic waveforms recorded by strong-motion stations are combined as static and dynamic triggers on a rate-and-state friction dependent quasi-dynamic spring slider model with shear-normal stress coupling. According to our results, earthquakes with Mw = 4 events noticeably advance in failure time. However, instant triggering occurs only when static stress loading is very high, and the fault is close to fail, explaining the delayed triggering observed SE of Samos Island. Simulations also revealed that the shear-normal stress coupling increases static loading but does not affect the dynamically controlled failure time advances observed at the end of the seismic cycle. After the earthquake, some of the faults adjacent to the rupture are more likely to fail, especially the long strike-slip fault segment capable of generating large earthquakes at the western edge. On the other hand, the Samos earthquake induced no significant dynamic triggering on far away faults near Izmir

Testing the normality of the residuals of surface temperature data at VLBI/GPS co-located sites by goodness of fit tests

Evaluating the distribution patterns of surface temperature data at Very Long Baseline Interferometry (VLBI)/Global Positioning System (GPS) co-located sites w.r.t. normality is one of the most important issues in modeling surface temperature data over long periods. Such evaluation can generate algorithms for filling in missing data at measurement sites. Some algorithms in the literature, such as those in the study of Cho et al. J Coast Res 65. doi: 10. 2112/SI65-321. 1, (2013), require trend, harmonic, and residual components to fill in the missing data. Trend and harmonic components estimate an optimal model that can be used to assist such algorithms when filling in missing data. The present study is based on the investigation of the normal distribution of the residuals of a surface temperature time series at VLBI/GPS co-located sites, after removing the trend and seasonal effects through harmonic components (inter-daily variations). This study uses surface temperature data collected from the VLBI/GPS co-located sites of two different regions in Europe: Matera (Italy) and Wettzell (Germany). The data collected from these sites form a time series, and time series analyses and conventional k-sigma outlier detection are implemented on these data sets before subjecting them to goodness of fit tests for normality. The residual components of the time series are acquired through a decomposing trend and signal effect from the original time series, assuming that the residuals of the time series are normally distributed. In testing the hypothesis that an observed frequency distribution fits the normal distribution, the following tests are used: Pearson chi (2), Kolmogorov-Smirnov, Anderson-Darling, Shapiro-Wilk or Shapiro-Francia, D'Agostino, Jarque-Bera, skewness, and kurtosis tests. Some graphical methods are also applied to support the results of the goodness of fit tests for normality. Some proposals on the application of the goodness of fit tests are put forward, such as the evaluation of the estimation model for trend and harmonic components by considering the properties of the implemented goodness of fit tests. The results of this study can be used to determine the optimal model for estimating trend and harmonic components. The output of the present study is expected to have an important role in modeling surface temperature distributions at co-located VLBI/GPS sites for filling in missing data. Above all, meteorological data, such as temperature, pressure, and humidity, are of specific interest for modeling tropospheric delay, the main error factor in positioning in space geodesy, which in turn makes investigations on the distribution of meteorological data more attractive in geoscience

Characteristics of the 2020 Samos earthquake (Aegean Sea) using seismic data

© 2021, The Author(s), under exclusive licence to Springer Nature B.V.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 < 1 km. Slip is confined in mainly two asperities, both located up-dip from the hypocenter and at shallow depths. The average displacement is ~ 1 m and the peak slip is ~ 3.5 m for a shear modulus of 3.2e10 N/m2. While it is difficult to constrain the rupture velocity in the inversions, the model suggests a slow rupture speed of the order of 2.2 km/s. The resolved source duration is ~ 16 s, compatible with the ~ 32 km length of the fault that ruptured