The earthquakes that struck in the early morning and early hours of Sunday in Athens caused upset for many residents of the capital.

It all started at 03:22 in the morning, when a2.7 Richter earthquake occurred with an epicenter two kilometers south-southwest of Halandri, while the tremor had a focal depth of 7.6 kilometers. The “dance” of the Richter’s however continued until the morning, as 7 more weak tremors were recorded.

Although superficial and short in duration, the earthquakes were felt in many areas. Internet users who were awakened by the initial tremor described it as quite frightening, as it was preceded by intense rumbling that woke them from their sleep. But is there any real cause for concern? Protothema.gr contacted three seismologists, Mr. Athanasios Ganas, Mr. Kostas Papazachos and Mr. Efthymios Lekkas, who appear reassuring about the phenomenon and tell us all we need to know.

Athanasios Ganas

“The Attica basin is an area of low seismicity. In the last decade we have had only three (3) surface earthquakes with magnitudes up to M3.6 in Metamorfosi (September 12, 2021). This is due to the fact that the major faults are located around it, i.e. the Parnitha fault that gave the earthquakes in 1999 and 2019, the Dionysos – Penteli fault, the Aphidna fault, the Thriasio fault and other smaller ones. Contrary to earlier opinions, I do not consider the Kifissos fault with a NE-SW direction to be active. The sporadic seismicity that occurs within the basin is due to the action of smaller faults that are sub-parallel to that of Parnitha, i.e. have a NW-SE direction. This direction is consistent with the current stress field and deformation of the solid crust as determined by geodetic data (GPS). The seismicity of 2024 started on 11 December at 19:29 with the two weak earthquakes M2.3 and M2.8, centered in the area of Kato Halandri – Neos Psychiko and with a depth of 7-8 km. The sequence continued with 16 weak tremors until Saturday 28/12. These earthquakes occurred in a NW-SE arrangement between Kato Halandri and Papagos, i.e. transversely to the mountainous mass of Hymettus and at depths of 4-8 km and magnitudes ranging from M0.6 to M2.1. Today 29/12 at 03:22 local time a weak M2.7 tremor occurred from the same focal area (Kato Halandri – Neo Psychiko) and at a depth of 6 km. Until this afternoon 7 other weak tremors have been recorded. No earthquake had been recorded in the wider area since 30/5 of 2013, when a weak earthquake of M2.0 magnitude occurred with a focus on Goudi. The almost linear epicentre pattern extends over a length of 6-8 km but we have no geophysical data to support the existence of a fault of this length, so it is more likely that there is a zone of smaller faults (lengths 1-2 km) in a NW-SE direction which has been activated due to fluid movement in the upper part of the solid crust. In any case, I am not worried about a major earthquake and I note that most of the buildings in the Basin are built with seismic regulations that exceed the requirements of seismic protection”

Kostas Papazachos

“Lately we have a persistent microseismic activity in western Athens (Chalandri, Cholargos, Neo Psychiko, etc.), from some unknown, probably small fault, which is apparently located in the northwestern outskirts of Hymettus, hidden under the sediments of the basin. So let’s answer 3 obvious questions from citizens:

What we know about seismic activity in Athens: Athens is a low seismicity area of the Greek territory (it belongs to the lower seismic risk zone of the Greek Seismic Regulation). All historical and instrumental seismological data, as well as the relevant geological-neotectonic information, show that the central and southern part of Attica is of very low seismicity and is not associated with any significant fault or even a strong earthquake since ancient times.

What we don’t know about seismic activity in Athens: There is no universally accepted methodology to safely estimate the evolution of activity for micro-sequences such as the one now underway. In other words, although there is research, there are no accepted operational tools to tell if an activity can lead to a strong earthquake.

If we don’t know exactly how the activity will unfold, what can we tell the citizens of Attica about the sequence that is underway: The Greek area has continually had countless similar sequences of microseismic activity without any strong seismic tremor. Besides, at least half of the strong earthquakes (above M=6.0) have no detectable foreshocks. Most likely, the seismic activity will gradually fade away in the coming weeks (rarely maybe even months). However, it is not unlikely to have the generation of similar or even stronger earthquakes within this sequence, which will logically worry Athens again.

In any case, it is not normal for a micro-sequence to upset (apart from some physical concern) a city that is in one of the (seismologically) quietest areas of Greece. The current seismic activity should simply remind us that seismicity is an integral part of the Greek space. And as I have already written in an earlier article: “…prevention and sober management (and not panic) must be the basis of civil protection … both in relation to earthquakes …, and of course in relation to all other … natural disasters …”. Let us therefore take the basic measures of self-protection and make sure that we live in houses with seismic capacity (as provided for by the existing legal framework of our country), so that whenever we receive a more powerful earthquake we will suffer the least consequences, regardless of the occasional generation (or not) of a small earthquake sequence near us.”

Ethymis Lekkas

“These earthquakes do not inspire any concern because they are on the Greek arc, there is high seismicity but they maintain a magnitude below 4 Richter which does not worry us”.