Coulomb stress has become a key point of discussion in assessing the seismic risk around Santorini, particularly following statements by Greek seismologist Akis Tselentis. where he cited it as a key factor in his risk assessment in relation to Santorini earthquakes.
In his analysis of the ongoing seismic activity in the region, Tselentis emphasized the role of Coulomb stress in determining whether the major Amorgos fault in the region is at risk of activation. While he noted that current calculations suggest negligible stress on this fault, he cautioned that its activation remains a possibility.
Understanding Coulomb Stress
Coulomb stress describes how stress redistributes within the Earth’s crust after an earthquake or magma movement. Coulomb-stress theory has been used for years in seismology to understand how earthquakes trigger each other.
It is based on the Coulomb failure criterion, which states that a fault will slip when the shear stress (the force pushing the fault to move) exceeds its resistance (friction and normal stress).
When an earthquake or volcanic activity occurs, it redistributes stress in surrounding areas. In some cases, this increases the likelihood of another earthquake by bringing a fault closer to failure. In other cases, it reduces stress, effectively delaying seismic activity, according to the US Geological Survey.
How Scientists Use Coulomb Stress to Assess Earthquake Risk
Seismologists use Coulomb stress transfer models to predict how one earthquake can influence another in nearby fault systems. This approach has been applied in several major seismic events.
In Santorini and according to Tselentis, magma movement beneath the Kolumbo volcano is exerting pressure on upper geological layers and the crust, which in turn triggers multiple smaller faults in the area. Tselentis estimates that this stress buildup could, under certain conditions, lead to a magnitude 6 earthquake if a specific fault in the seismogenic zone becomes critically stressed. This being said, the seismologist notes that the major fault in the area, the Amorgos fault, has not yet been activated.
Limitations and Debate Over Coulomb Stress Models
While Coulomb stress analysis is a widely used tool in seismology, it remains the subject of debate. A 2020 study published in Scientific Reports (Nature) used a case study to examine whether Coulomb stress changes significantly influence the Gutenberg-Richter law, which describes the statistical relationship between earthquake magnitude and frequency. The study found that Coulomb stress does not significantly alter this fundamental relationship, suggesting that while useful, it may not be a definitive predictor of future earthquakes.
Other key limitations of Coulomb stress models include:
- Complex Fault Interactions – Stress redistribution is not uniform, and faults may respond in unpredictable ways
- Time Uncertainty – Coulomb stress models often assume instantaneous stress changes, but real-world seismic events can unfold over months, years, or even decades
- External Factors – Volcanic activity, fluid pressure changes, and crustal variations can all influence fault stability, beyond what Coulomb stress models account for
Greek seismologists, while differing in their assessement and predictions of the situation in Santorini, have all embraced the need for a holistic and data-based assessement of the ongoing seismic swarm near Santorini and estimate that the situation could continue unabated for months.
Tselentis and Santorini Earthquakes Risk
Tselentis recently resigned from the National Committee for Seismic Risk Assessment, citing political interference in scientific work.
In his public statements, he expressed concerns over the ongoing seismic activity around Santorini, emphasizing the potential activation of faults in the region. His warnings have fueled debate over the Greek government’s handling of the seismic risk and the scientific independence of earthquake monitoring efforts in the country.
