The 19 July 2019 earthquake in Athens, Greece: A delayed major aftershock of the 1999 Mw = 6.0 event, or the activation of a different structure? (original) (raw)

The Athens 1999 mainshock (Mw=5.9)and the evolution of its aftershock sequence

Bulletin of the Geological Society of Greece

The spatial distribution of the aftershocks that followed the September 1999 mainshock (Mw=5.9), which caused severe damage and loss of life in the nearby city of Athens, is examined in the present work. Ρ and S arrivals of seismic waves recorded by the permanent seismic network as well as by a number of digital seismographs and accelerographs, which had been deployed in the broader epicentral area shortly after the mainshock occurrence, were used for the determination of the focal parameters of the mainshock and its aftershocks. The spatial distribution of the aftershocks led to the recognition of the fault, which produced the September mainshock, while certain features of the rupture process may be deduced on the basis of their spatiotemporal variation

The Egion June 15, 1995 (6.2 M L ) earthquake, western Greece

Pure and Applied Geophysics, 1996

On June 15, 1995 at 00:15 GMT a devastating earthquake (6.2M L ) occurred in the western end of the Gulf of Corinth. This was followed 15 min later by the largest aftershock (5.4M L ). The main event was located by the University of Patras Seismological Network (PATNET) at the northern side of the Gulf of Corinth graben. The second event (5.4M L ) was located also by PATNET near the city of Egion, on a fault parallel to the Eliki major fault that defines the south bound of the Gulf of Corinth graben. A seismogenic volume that spans the villages of Akrata (SE) and Rodini (NW) and extends to Eratini (NE) was defined by the aftershock sequence, which includes 858 aftershocks of magnitude greater than 2M L that occurred the first seventeen days. The distribution of hypocentres in cross section does not immediately suggest a planar distribution but rather defines a volume about 15 km (depth) by 35 km (NW-SE) and by 20 km (NE-SW).

Did the 7/9/1999 M5.9 Athens Earthquake Come with a Warning?

2002

Prior to the 7/9/1999 MS = 5.9 Athens earthquake, regional seismicity has exhibited a power-law increase, of the form  = ΣΩ = K+A(tc−t)^n, where Ω is estimated using an expression logΩ  = cM + d and tc is the time of the culminating event. Such changes appeared after the 17/8/1999 M7.4 Izmit event. We quantified the performance of the power law vs. the null hypothesis of constant seismic release rates, by defining the curvature C as the ratio of the power law fit RMS/linear fit RMS, so that the smaller C is, the better the power law behaviour. By mapping C, we have established a critical radius of 110 km and observed that the region of correlated accelerating seismic release extended from the N. Aegean, through Euboea and Attica to the SW Peloponnese. A few days prior to the Athens event, min(C) was centred at the epicentral area and numerical simulation yielded tc = 1999.676 and predicted MS = 5.77. Seismicity rates returned to normal (quasi-constant) after the Athens event.We interpret this effect as critical point behaviour, following remote excitation of a broad area by stress redistribution due to the Izmit event which, at Athens, has triggered ‘premature’ failure of a fault nearing its load bearing capacity. If this is correct, we have documented a case of remote earthquake triggering by another earthquake, as well as insight into the mechanisms producing it. As a corollary, we note that a large event may beget another large event in its broader region of interaction, which may be preceded by characteristic precursory seismicity changes.

The Crete Isl. (Greece) Mw6.0 Earthquake of 27 September 2021: Expecting the Unexpected

GeoHazards, 2022

The 27 September 2021 damaging mainshock (Mw6.0) is the first known strong earthquake that ruptured the Arkalochori area, Crete Isl., Greece, during the entire historical period, making it an unexpected event in the long-term sense. The area is characterized by the presence of the normal active Kastelli Fault (KF) striking NNE-SSW and dipping towards ~WNW. The KF, of surface exposure only ~6 km, at its southern tip is truncated by the nearly perpendicular active Nipiditos fault. The main shock was preceded by foreshock activity lasting for ~3.9 months, thus the mainshock turned out to be an expected event in the short-term sense. Maximum ground subsidence of ~20 cm was estimated from InSAR images, but this also incorporates deformation that may have been caused by the largest aftershock (Mw5.1) of 28 September 2021. The fault model produced from the inversion of InSAR observations indicated strike 216°, dip towards ~NW at angle 53°, rake −95°, and is consistent with fault-plane solu...