New model finds complex earthquake patterns of the Phlegraean Fields near Naples

New model finds complex earthquake patterns of the Phlegraean Fields near Naples

The Phlegraean Fields volcanic complex, situated beneath the bustling metropolitan area of Naples in Italy, has been experiencing significant ground uplift since 2005, accompanied by an increasing number of minor earthquakes. This phenomenon has garnered considerable attention within this densely populated region. While phases of uplift and subsidence have been documented for over a millennium, the intricate relationship between ground uplift and seismic activity remains only partially understood.

A recent study published in Communications Earth and Environment provides valuable insights into the long-term patterns of earthquake activity in the area. The researchers found that the ongoing trend can be effectively elucidated by considering both changes in stress within the Earth's crust and the frictional behavior of geological faults. Moreover, they were able to partially account for the observed swarms of earthquakes through the interactions among individual seismic events, modeling them as layered sequences of aftershocks.

The research team, led by PD Dr. Sebastian Hainzl from the GFZ Helmholtz Centre for Geosciences, successfully replicated earthquake patterns observed in the past decades by integrating both long- and short-term modeling techniques. Their analysis utilized earthquake catalogues and elevation measurements dating back to approximately 1905. A validation test demonstrated that the model is also applicable for short-term probabilistic predictions, specifically regarding anticipated earthquake rates and maximum magnitudes over timeframes ranging from weeks to months. This study offers a significant advancement in tools for more accurately assessing seismic hazards in the Campi Flegrei region.

Uplift cycles in Campi Flegrei

Beneath the conurbation of Naples, home to approximately 900,000 residents, lies a sophisticated magmatic system that includes various reservoirs within the Earth's crust and upper mantle. For centuries, Campi Flegrei has been characterized by recurring phases of ground uplift and subsidence driven by magmatic and hydrothermal processes, often leading to increased seismic activity. Occasionally, these cycles culminate in volcanic eruptions that result in the formation of new maars or cones. The last eruption recorded took place in 1538 at Monte Nuovo, following a series of uplift phases between 1400 and 1536 that closely resemble current conditions.

Since 2005, the ground in the area has risen by more than a meter, raising alarm due to the substantial population density. Historical records indicate similar uplift phases occurring throughout the 20th century, particularly during the periods of 1950–52, 1969–72, and 1982–84, which resulted in evacuation measures due to heightened seismic activity.

New study examines seismicity patterns of the region

In this comprehensive study, PD Dr. Hainzl, alongside Prof. Dr. Torsten Dahm, head of the same section, and Dr. Anna Tramelli from the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV), explored the unique seismicity patterns present in the Phlegraean Fields. Their investigation utilized data sourced from earthquake catalogues and surface deformation measurements.

The seismicity information was compiled from a variety of catalogues: since 2005, data from the local catalogue detailing duration magnitudes has been provided by the Observatorio Vesuviano, while a broader historical perspective has been drawn from the HORUS catalogue of homogenized moment magnitudes for earthquakes in Italy dating back to 1960.

Long-term developments: Ground uplift and earthquakes

The findings indicate a significant correlation between seismic activity and ground uplift in Campi Flegrei. Nonetheless, this relationship is not simply linear; since 2005, earthquake activity has displayed a distinctly nonlinear and accelerated response. The researchers identified that the Kaiser effect from rock mechanics can elucidate the foundational relationship between uplift and seismic activity, yet it does not fully account for the escalation of seismic events observed since 2005.

Short-term developments: Earthquake swarms

While the long-term seismicity trends correlate with ground uplift, this correlation does not extend to the short-term phenomena observed in swarm earthquakes. These swarms likely arise from episodic fluid intrusions and interactions between earthquakes. Hainzl explains, "We were able to show for the first time that these earthquake swarms can be explained, at least in part, by interactions between individual events and that they possess typical characteristics of tectonic aftershock sequences."