Seismicity and Orange Alerts in the Campi Flegrei (Naples, Campania Region)

Naples (Campania), southern Italy, is located in a seismically active region known for its proximity to the Campanian volcanic arc and the presence of the active Mount Vesuvius volcano. This region is part of the broader Mediterranean seismic belt, which is characterized by a high level of tectonic activity due to the convergence and subduction of the African and Eurasian tectonic plates. The seismicity in Naples and the surrounding Campania region is primarily driven by the interaction of these tectonic plates, which results in the movement of the Earth's crust and the release of energy in the form of earthquakes.

On the 6^th of October 2023, Quantectum issued the orange alert for the Naples area (Campania region) due to increased seismic activity that was affected by the regional increase of shear traction and local instabilities in the following days. The heightened earthquake activity was associated with the growing volcanic activity located in the Campi Flegrei area. Evacuation plans were already prepared for the deterioration of the situation.

In this blog, we will describe the geological setting and seismicity of the Naples area, as well as our forecasting model results, which suggest further potential earthquake triggering in the area.

Seismicity and Tectonic Setting in Campania, Italy 

Campi Flegrei, also known as the Phlegraean Fields, is a large volcanic caldera located west of Naples, Italy. It is one of the most significant and well-known volcanic systems in Italy. The term "caldera" refers to a large, collapsed volcanic crater, often formed by the explosive eruption and collapse of a magma chamber. It is notable for its geologic complexity, volcanic history, and the potential for volcanic and seismic activity in the region. It has a long history of volcanic eruptions and ground uplift events.

The volcanic and geothermal activity in the Campi Flegrei is closely associated with seismic activity. The movement of magma and the pressure exerted by underground fluids trigger earthquakes in the region that can vary in magnitude and impact.

Picture 1: Map of the geological setting of the Caldera of the Campi Flegrei (credit: Sacchi et al., 2019).

Picture 2: Map of the Campi Flegrei caldera (Naples, Italy), seismic stations, and monitoring sites for analysis of different geochemical and geophysical parameters in the volcanic area (credit: Sabbarese et al., 2020).

Moreover, the tectonic setting in the Naples region is complex and is primarily characterized by the convergence of several tectonic plates, including the African Plate, the Eurasian Plate, and the Adriatic Plate. The interaction and collision of these plates create a dynamic geologic environment, leading to various geologic features and seismic activity in the region:
- The African plate is to the south of Italy and is moving northward, converging with the Eurasian plate. This convergence is a major driving force for the tectonic activity in the region.

- The Eurasian Plate extends northward from the Mediterranean Sea into Europe. The collision and subduction of the African Plate beneath the Eurasian Plate in the Mediterranean region create significant tectonic stress and deformation.

- Adriatic plate is a smaller microplate and is involved in the complex tectonic interactions in the region and influences the geology of southern Italy, including the Naples area.

The convergence and interaction of these tectonic plates give rise to several key geologic features and phenomena in the Naples region. 

The Phenomenon of Bradyseism and Its Activity

The area of the Campi Flegrei is characterized by the phenomenon of bradyseism, which consists of a slow movement of raising and lowering the soil, related to changes in the volcanic system such as the increase in temperature and pressure in the rocks of the subsoil. Those determine the lifting of the area and besides being associated with eruptions they can also cause ground shaking.

The evolution of bradyseism over the centuries, and the presence of lithdoms testifies to the slow process of lowering the area, which began in post-Roman times. For example, in the period of maximum lowering - probably dating back to the Middle Ages - some studies show that the ground level was between 7 and 10 meters lower than at the time of construction of the Serapeum in the first century.

In the period from 1969-72 and 1982-84, there were two bradyseism crises in the form of a rise of 1,70 meters and then an increase of about 1.80 meters (total lifting of the soil of 3.5 meters) This phenomenon was accompanied by high seismic activity in which more than 10,000 earthquakes were recorded, the strongest of them being M4.2 that occurred on the 4^th of October 1983. In the process, a part of the population of Pozzuoli was evacuated due to the risk of collapses caused by strong seismic activity.

Since 1985, the soil has started to fall again, although with shorter and smaller lifting periods. These periods are punctually accompanied by seismic swarms, the last of which occurred in June 2010.

Orange Earthquake Alert for the Naples (Campania)

On the 7^th of September 2023, a magnitude 3.8 tremor occurred at the epicenter in Pozzuoli, making it the largest tremor in the last 39 years. From January 2023 until November 2023, about 1,500 tremors have already been recorded, putting in front the "intense bradyseism crisis".

The Italian government issued a yellow alert at the beginning of October due to the increased volcanic activity for the Campi Flegrei. The alert level is established periodically following the monitoring of the due parameters considered by the Civil Protection and Institute of Geophysics and Volcanology, INGV.

Since the 21^st of August 2017, the Campi Flegrei area (Campania) has been characterized by an almost perfect geometric Increasing Seismicity Sequence (ISR) that had a potential continuation between the 9^th of October 2023 and the 8^th of November 2023, as shown in the picture below. ISR implies that there was a pattern of increasing seismic activity in the region. Geometric, in this context, likely refers to the idea that the increase in seismic events followed a mathematical or geometric progression, such as an exponential growth pattern.

Picture 3: Increasing Seismicity Sequence (ISR) for the Campi Flegrei area from August 2017 to November 2023.

The examination of T-synchronizations within the Campi Flegrei area indicated that the next T-synchronization would likely occur sometime around the 20^th of October 2023, with a margin of error of approximately plus or minus 4 days. This estimation is derived from a study of the historical data and patterns associated with T-synchronizations in the area, providing a reasonably accurate timeframe for this seismic event.

Picture 4: T-synchronizations within the Campi Flegrei area.

Furthermore, the analysis of the most recent three seismic events within the ongoing ISR sequence provided a noteworthy insight into the potential for a seismic event of magnitude 4.0 or higher. This forecasting analysis indicates that there was a heightened likelihood of such an event occurring within the timeframe of the 26^th of October 2023 and the 5^th of November 2023, as shown in the picture below.

Picture 5: Potential for a seismic event of magnitude M4 or higher in the Campi Flegrei area, Italy.

Quantectum's earthquake forecasting models furthermore identified an increase in shear traction, which is essentially the force acting parallel to a fault plane. This change in the geophysical landscape was directly attributed to the occurrence of a rotational singularity after the 8^th of October 2023, in the region of southern Italy. The rotational singularity is a term used in geophysics to describe a point in space and time where rotations or angular displacements are particularly pronounced. In this case, it implies a unique geological event that has unfolded in the area.

The increased shear traction and the rotational singularity's influence on the geological conditions have acted as triggering mechanisms for additional earthquakes within the ongoing sequence.

Picture 6: Increased shear traction and rotational singularity's influence on triggering Naples's earthquakes.

The utilization of Ultra-High-Definition (UHD) models to monitor and understand local instabilities in the Campania region provided valuable data about seismic instability in the area. According to these UHD models, the maximum level of these instabilities was projected to commence after the 8^th of October 2023, marking the beginning of a phase where the geological dynamics in the region are expected to undergo notable changes. The highest values of these instabilities were reported to be reached on the 21^st of October 2023, when the geological conditions in the Naples region were expected to be particularly dynamic and prone to seismic activity or other earth-related events.

Picture 7: The Ultra-High-Definition models of the local instabilities in the region of Campania.

Mb4.1 Earthquake in Thyrennian Sea, Naples, Italy (27^th of October 2023)

In the wider area where we issued a yellow earthquake alert a magnitude 4.1 earthquake actually occurred on the 27^th of October 2023, at 00:22 local time, at a depth of 413 km (256.6 mi), according to the EMSC.

Picture 8: Location of the Mb4.1 earthquake in the Naples region on the 27^th of October 2023.

The joint graph of the shear traction (red line) and dynamic traction field (blue line) below indicates the earthquake occurred during a strong increase in these fields. Both started a few days before the seismic event and the shear traction field was expected to continue to rise in the following days due to the presence of tectonic waves. The elevated dynamic traction field signifies that the propagating tectonic waves were also active. In other words, multiple earthquakes occurred along them, which contributed to the strengthening of the dynamic traction values.

Picture 9: Shear traction and dynamic traction field in the Naples area, Italy.

The following map illustrates the setting of the tectonic waves that contributed to the earthquake triggering in the Tyrrhenian Sea and the increasing shear traction field around the epicenter and its wider area. The propagation and interaction of these waves in the Tyrrhenian Sea region have contributed to the buildup of stress and energy along fault lines, a critical precursor to seismic events. The map provides a snapshot of the tectonic framework, highlighting the fault lines and plate boundaries where this energy is concentrated.

Picture 10: Tectonic waves setting that triggered Mb4.1 earthquake in Naples, Italy.

Furthermore, the map below displays the earthquake-triggering potential, indicating that the earthquake occurred at the edge of a tectonically unstable region and the influence of the strengthening shear traction field. The Earth's lithosphere is composed of a mosaic of tectonic plates, each with its own distinct boundaries and movements. Along these boundaries, stress and strain accumulate over time, making them prone to sudden release in the form of earthquakes. The map adeptly portrays this aspect by pinpointing the epicenter of the earthquake at the edge of a tectonic boundary.

Picture 11: Earthquake-triggering potential in the Campania region, Italy.

Quantectum issued a report about the weekly seismic activity and the tectonic traction variations on X Quantectum Euro-Mediterranean region profile where this seismic event was also mentioned. It is accessible here.

Lastly, we issued earthquake alerts for the area of southern Italy due to the strengthening processes in the Earth’s crusts, which lead to elevated tectonic tractions and enhanced instability of the fault system but we also monitor the variations in the tectonic waves’ activity.

Conclusion

Quantectum will continue its constant and careful monitoring of the Campania region (Campi Flegrei), due to expected further earthquakes related to the recent volcanic activity that has increased and is constantly monitored by INGV.

Our models show a perfect Increasing Seismicity Sequence geometry which, associated with an increase in shear traction crossing southern Italy, suggests the increased probability of a seismic event (already mentioned in recent weeks) in the coming weeks. To be more precise, an increase in seismicity is expected in the period from the 9^th of October to the 8^th of November 2023. Based on these analyses and the use of our models, we issued the orange alert for the Campi Flegrei area (Campania) a few weeks ago.

Sources:
1) Ingenio. 2023. Campi Flegrei: un viaggio nella storia e nelle caratteristiche geologiche di quest'area vulcanica. Accessed on 03-Nov-2023. Available at: https://www.ingenio-web.it/articoli/campi-flegrei-un-viaggio-nella-storia-e-nelle-caratteristiche-geologiche-di-quest-area-vulcanica/#:~:text=Quando%20parliamo%20di%20Campi%20Flegrei,depressa%20nota%20come%20%22caldera.%22
2) Distar. Campi Flegrei. Accessed on 05-Nov-2023. Available at: https://www.distar.unina.it/it/vulcani-napoletani/campi-flegrei
3) Protezione Civile. Fenomeno di bradisismo. Accessed on 03-Nov-2023. Available at: https://www.protezionecivile.gov.it/it/approfondimento/fenomeno-di-bradisismo/
4) l'Unita. 2023. Cos’è il bradisismo, il fenomeno nei Campi Flegrei a Napoli e Pozzuoli tra terremoti ed eruzioni. Accessed on 03-Nov-2023. Available at: https://www.unita.it/2023/09/26/cose-il-bradisismo-il-fenomeno-nei-campi-flegrei-a-napoli-e-pozzuoli-tra-terremoti-ed-eruzioni/
5) Sacchi, M., De Natale, G., Spiess, V., et al. 2019. A roadmap for amphibious drilling at the Campi Flegrei caldera: insights from a MagellanPlus workshop. Sci. Dril., 26, 29–46, https://doi.org/10.5194/sd-26-29-2019. Available at: https://sd.copernicus.org/articles/26/29/2019/
6) Sabbarese, C., Ambrosino, F., Chiodini, G., et al. 2020. Continuous radon monitoring during seven years of volcanic unrest at Campi Flegrei caldera (Italy). Scientific Reports, 10(1), 9551. Available at: https://www.nature.com/articles/s41598-020-66590-w

Appendix

The map below shows earthquakes that occurred in the wider region of Campi Flegrei during the time window from the 1^st of January 2000 until the 7^th of November 2023. The strongest were:
- Mw4.3 on the 30^th of May 2008,
- Mw4.3 on the 21^st of August 2017,
- Mw4.1 on the 26^th of October 2023,
- Mw4.3 on the 14^th of November 2023.

Picture 12: Earthquakes that occurred in the wider region of Campi Flegrei from the 1^st of January 2000 until the 7^th of November 2023.

The map shows earthquakes that occurred in the wider region of Campi Flegrei during the time window from the 1^st of January 2023 until the 7^th of November 2023.

Picture 13: Earthquakes that occurred in the wider region of the Campi Flegrei from the 1^st of January 2023 until the 7^th of November 2023.